ludeful: no definition. It appears to have appeared only once in history. (poss. lewdful)
mediatized: to annex a state or territory while preserving some of its ruler’s rights
franked: marked in such a way as to secure transmission or passage
gobonated: in heraldry, equal divisions forming squares (gobbets)
foliot: a mischevious woodland creature in Italian folklore
exornation: ornamentation or embellishment
chiromancy: palmistry and fortune-telling
sithence: archaic version of “since”
cit: 17th century slang for citizen
pelf: a scornful term for wealth
antbear: an aardvark
avaunt: begone

morganatic: a marriage in which title or property will not be shared or bequeathed
lappet: a small flap or loose piece hanging from a piece of clothing; also, a wattle
supererogate: to do more, or perform better, than is required or expected
vedette: a mounted or mobile advance unit posted close to enemy lines
megrims: low spirits, a migraine, or some other transitive discomfort
unregenerate: unconvinced, unconverted, or unrepentant
sal volatile: ammonium carbonate (smelling salts)
omniana: information relating to… everything
intagli: incised carving, as oppose to relief
objurgate: to berate, reprimand, or curse

geognostic: having to do with the constituent parts of the earth (air, crust, etc)
cantatrice: a professional female singer (clearly, but an uncommon word)
dysgenic: having a negative effect on the offspring - opposite of eugenic
historiographer: an official historian of an institution, order, or society
crenated: having a notched or rounded saw-tooth pattern at the edge
plangent: resounding loudly, especially with a sad or plaintive noise
epos: an epic poem, or events which would be appropriate for one
faience: glazed earthenware; also, a strong greenish-blue color
monody: limited to or dominated by a single voice or melody
hygrometry: the branch of physics concerned with humidity
aseity: the property of being self-created or self-originating
ataraxy: the state of being emotionally undisturbed, calm
bibelot: a decorative object, trinket, or curiosity
commorient: dying simultaneously or together
conspectus: a general survey or summary

syndic: a representative for a corporation or university; also, certain civil magistrates
pyx: a container for the eucharist; also, a container for specimen coins at a mint
lipsanotheca: the container inside a reliquary which contains the relic
mora: a unit of time equal to a short syllable (a poetic metric)
autochthonous: born of the earth; sprung from the ground
inenubilable: indistinct; unable to be made clearly visible
matross: obsolete term for an artillery gunner’s assistant
lief: beloved, or willing, or preferred
orgulous: proud, haughty

deliquium: chemically, dissolution into air or liquid. otherwise, a swooning or faint mood
ebullition: boiling up or pouring out, either emotionally, physically, or linguistically
peripety: corruption of peripeteia, a sudden turn of events, usually in literature
bruit: (noun) a din or loud noise. (verb) to voice loudly or spread rumor
trumpery: showy, deceptive, or nonsensical (from tromper, to deceive)
voluptuary: a person devoted to luxury and sensual pleasure
maunder: to talk or move about aimlessly or confusedly
insouciant: carefree, indifferent, or nonchalant

dulia: a theological term signifying the honor paid to the saints (as opposed to god)
lazaret: a small ship, room or building used for quarantine (or simply set aside)
disseizin: wrongful dispossession of one in the possession of real property
surplice: a loose-fitting garment with fabric crossing diagonally in front
quillon: one of the two protrusions forming the crossbar of a sword
opetide: early spring, when flowers’ buds are beginning to open
omnisubjugant: one to whom everyone else is subject (clearly)
anchorite: a hermit or one who has otherwise isolated himself
propinquity: nearness or similarity in time, place, or nature
gallimaufry: a medley or jumble (originally a food term)
legerdemain: sleight of hand (French: “light of hand”)
dandiacal: of or pertaining to dandies; foppish
aureate: gold, brilliant, or ornate in style
apposite: relevant, apt, or well-suited
guerdon: a reward or compensation
pleach: to interweave or braid
portreeve: a port warden

anacreontic: after the style of Anacreon, a Greek poet fond of women and drinking
tholus: a circular building with a conical or vaulted roof (Greek)
architrave: the lowermost molding at the top of a colonnade
gonfalon: a standard or banner hung from a crossbar
caique: a rowboat or small sailing ship
fiacre: a small, four-wheeled carriage
pardine: a leopard or panther
nigrescent: not quite black

Each and every one. Pitchman’s jargon. Avoid, except in dialogue.

Enormity. Use only in the sense of “monstrous wickedness.” Misleading, if not wrong, when used to express bigness.

Flammable. An oddity, chiefly useful in saving lives. The common word meaning “combustible” is inflammable. But some people are thrown off by the in- and think inflammable means “not combustible.” For this reason, trucks carrying gasoline or explosives are now marked FLAMMABLE. Unless you are operating such a truck and hence are concerned with the safety of children and illiterates, use inflammable.

In the last analysis. A bankrupt expression.

Lay. A transitive verb. Except in slang (“Let it lay”), do not misuse it for the intransitive verb lie. The hen, or the play, lays an egg; the llama lies down. The playwright went home and lay down.

Nauseous. Nauseated. The first means “sickening to contemplate”; the second means “sick at the stomach.” Do not, therefore, say, “I feel nauseous,” unless you are sure you have that effect on others.

Noun used as verb. Many nouns have lately been pressed into service as verbs. Not all are bad, but all are suspect.

People. The word people is best not used with words of number, in place of persons. If of “six people” five went away, how many people would be left? Answer: one people.

Prestigious. Often an adjective of last resort. It’s in the dictionary, but that doesn’t mean you have to use it.

Respective. Respectively. These words may usually be omitted with advantage.

The truth is… The fact is… A bad beginning for a sentence. If you feel you are possessed of the truth, or of the fact, simply state it. Do not give it advance billing.

Transpire. Not to be used in the sense of “happen,” “come to pass.” Many writers so use it (usually when groping toward imagined elegance), but their usage finds little support in the Latin “breathe across or through.” It is correct, however, in the sense of “become known.” “Eventually the grim account of his villainy transpired” (literally, leaked through or out).

-wise. Not to be used indiscriminately as a pseudosuffix: taxwise, pricewise, marriagewise, prosewise, saltwater taffywise. The sober writer will abstain from the use of this wild additive.

hypallage: a reversal of an expected phrasing (i.e. doing well -> well doing)
renversé: a French term, meaning something performed with a bent waist
toise: an old French unit of length equivalent to 6.4ft (almost exactly 2m)
quinsy: an outdated term for some forms of tonsil-related disease
obliquity: divergent - mathematically, astronomically, or mentally
iracundulous: a redundant addition to iracund (prone to anger)
tunicle: a garment worn by certain religious functionaries
meseraick: an anatomical term relating to the humors
eleemosynary: pertaining to or supported by charity
prolegomena: an introductory essay or preface
whilom: formerly or at one time

From Ten Thousand A-Year

pomatum: a perfumed unguent for the scalp (it’s pomade)
bedizen: to ornament or dress in a showy or pompous manner
opprobrious: expressing (or bringing) reproach or scorn
champerty: sharing the proceeds of a lawsuit by an outside party who has encouraged the
  litigation. Used to be illegal, is now the standard
animadversion: a critical or reproachful remark
jackanapes: an impudent person, especially a young man or child
fustian: a stout fabric of cotton and flax, or unnecessarily turgid language
virago: a strong and forward woman, or critical and scolding woman
palaver: to talk profusely or idly

From Glaucus; or, The Wonders of the Shore

congener: an organism belonging to the same class or group as another organism
coracle: a small boat made of wicker and a treated or waterproof material
sciolism: superficial knowledge, or a pretentious attitude of scholarship
tyro: a beginner or novice

metempsychosis: belief in reincarnation (as animals and plants included)
teraphim: household gods, worshiped by early Hebrews via idols
eidolon: a phantom, apparition, or idol

From the last hundred pages or so of The Life and Opinions of Tristram Shandy, Gentleman:

obtruncate: to deprive of a limb (makes sense).
indissoluble: perpetual or incapable of being dissolved or destroyed. I love double negatives within words.
oedematous: of or pertaining to the edema (obviously). Edema: interstitial cellular fluid.
sententious: given to pithy or moralizing sayings.
ratiocination: the process of logical reasoning.
aposiopetic: (aposiopesis) breaking off a sentence in the middle, as if unable to proceed
parallelogramical: parallelogram-shaped (clearly; I just liked the word).
radix: the base of a numerical system, or the root of a plant (interesting).
jactitation: a boast that causes harm to another, also extreme restlessness in bed?
delectation: enjoyment (knew it).
saturnine: sluggish, melancholy, or bitter in temperament.
farthingal: hoops used to expand women’s skirts at the time of the book.
palfry: (palfrey) a woman’s saddle, smaller and softer.
placket-hole: the hole that goes into a pocket (!).
concupiscence: sexual lust, or more generally, passion.
windlass: a sort of crank-based lifting machine (no idea).
geniture: birth.
costive: constipated, slow to act, or stingy (very versatile word!).
impuissance: (impuissant) weak, feeble.
captious: of a disposition to point out faults, or ensnaring and perplexing when referring to argument.
farrago: a mixture or medley.
pannier: a basket or bag (i.e. breadbasket), or again hoops to expand skirts.
basilicon: an ointment made of wax, pitch, resin, and oil or lard.
ecliptic, trine, and sextil: all terms to do with astrological positions.
argute: shrewd or subtle (I assume it has roots in the hundred-eyed god Argus).

It never occurred to me that the above oath, so benign and absurd in sound, is actually a corruption of “God’s hooks,” a euphemism for the nails in the cross. Gadzooks indeed!

From Burton’s translation of the 1001 Nights.

grammarye: corruption of “grammary” or vice versa. General knowledge or erudition.
nenuphar: the “great white water lily of Europe.” Okay…
blee: complexion.
carnelian: a type of red chalcedony made into jewelry. Was a descriptor for some lady’s lips.
wot: know. Variation of “wit.”
lout: bend or stoop low out of courtesy. (I know what the other lout is)
wassail: to drink someone’s health or revel in general with drink.
sworder: swordsman or fighter.
eyne: archaic plural of “eye.” Really now, you could just say eyes.
hent: to seize or grab.
garth: a courtyard or garden.
syce: a groom or stable boy.
viaticum: supplies for a journey - also when the Eucharist is given to one near death.
gugglet: see guglet > see goglet > a long-necked earthenware container for water or liquid.
dight: to dress or adorn.
limn: to portray or illuminate - originally to literally illuminate.
meseemeth: it seems to me. Obviously… but come on.

Did you ever notice that “broadcast,” when broken down, essentially means to “throw in a wide pattern?” Neither did I. And yet it makes so much sense. Start looking closely at everything about you and you find this sort of thing everywhere.