This section is from the book "Hill's Manual Of Social And Business Forms: A Guide To Correct Writing", by Thos. E. Hill. Also available from Amazon: Hill's Manual Of Social And Business Forms: The How-To-Do-Everything Book Of Victorian America.
Invalidate - weaken, injure, destroy, overthrow.
Invective - censure, abuse, railing, reproach, satire.
Invent - feign, fabricate. frame, conceive, discover, devise.
Invest - enclose, surround, confer, adorn, array, endow, endue.
Investigation - search, inquiry, examination, scrutiny, research.
Inveterate - obstinate, confirmed, constant, fixed.
Invigorate - restore, strengthen, fortify.
Invincible - unyielding, unconquerable.
Involve - envelop, enwrap, entangle, implicate.
Irascible - irritable, hasty, fiery, hot, angry.
Ire - anger, temper, wrath, passion, resentment.
Irony - ridicule, sarcasm, satire, burlesque.
Irrational - unreasonable, foolish, absurd, silly.
Irrefragable - undeniable, indisputable, incontrovertible, unquestionable.
Irritate - plague, anger, tease, excite, provoke, aggravate, exasperate.
Irruption - opening, invasion, inroad, bursting forth.
Issue - offspring, progeny, result, end, sequel, egress, evacuation, effect, consequence.
Jade - harass, weary, tire, dispirit.
Jealousy - suspicion, envy.
Jest - fun, joke, sport.
Jocose - funny, witty, merry, jocular, pleasant, facetious, waggish.
Jocund - joyful, lively, merry, gay, sprightly, sportive, light-hearted, vivacious, mirthful.
Join - unite, add, combine, close, adhere, confederate league.
Joke - rally, sport. Jollity - hilarity, mirth, gayety, merriment, festivity, joviality.
Journey - travel, trip, voyage, tour.
Joy - happiness, delight, gladness, charm, rapture, ecstasy, felicity, exultation, pleasure, transport.
Judgment - sentence, decision, doom. opinion, discernment, discrimination, penetration, intelligence, sagacity.
Just - exact, accurate, correct, honest, barely, upright, righteous, equitable, incorrupt.
Justify - defend, excuse, clear, absolve, maintain.
Justness - exactness, correctness, accuracy, equity, propriety.
Keen - sharp, penetrating, acute, cutting, piercing, shrewd.
Keep - hold, detain, support, retain, maintain, guard, reserve, sustain.
Kind - indulgent, compassionate, tender, lenient, gentle, affable, courteous, benignant, bland.
Kind - sort, manner, class, race, species, way, genus.
Knowledge - understanding, perception, learning, erudition, skill, acquaintance.
Labor-toil, work, strive, exert, drudge.
Lament - sorrow, mourn, deplore, complain, bewail, grieve, regret.
Languid - weary, weak, faint, exhausted, dull, drooping.
Large - comprehensive, capacious, extensive, big, great, huge.
Lassitude - prostration, languor, weariness, enervation, fatigue.
Last - latest, hindmost, ultimate, final, end.
Lasting - durable, continuous, forever, continual, permanent, perpetual, eternal.
Latent - unseen, hidden, secret.
Laudable - praiseworthy, commendable.
Laughable - droll, ridiculous, comical, mirthful.
Lavish - profuse, wasteful, extravagant.
Lazy - indolent, idle, slothful, inactive.
Lean - bend, incline, totter, waver.
Learning - intelligence, knowledge, erudition, science, literature, information.
Leave - abandon, desert, resign, relinquish, bequeath.
Legitimate - real, legal, lawful, genuine.
Lengthen - protract, extend, continue, draw out.
Lessen - diminish, decrease, abate, reduce, subside, shrink, degrade.
Let - allow, permit, suffer, leave, hire.
Lethargic - dull, tired, weary, heavy, drowsy, sleepy.
Level - even, smooth, plain, flat.
Levity - giddiness, gayety, fickleness, vanity, lightness.
Liable - exposed, responsible, subject.
Liberal - benevolent, generous, munificent, charitable.
Liberate - free, set free, deliver, release.
Lle - deception, untruth, fiction, fabrication, falsehood.
Life - being, energy, vitality, vivacity, briskness.
Lifeless - deceased, dead, inanimate, inactive, stale, flat, dull.
Lift - raise, elevate, exalt, hoist.
Light - illuminate, enlighten, nimble, kindle.
Like - probable, similar, uniform, resembling.
Likeness - resemblance, picture, portrait.
Liking - inclination, attachment, fondness, affection.
Linger - wait, delay, loiter, hesitate, saunter, tarry, lag.
Liquid - fluid, liquor. Listen - hearken, attend, hear, overhear.
Little - small, diminutive. Live - exist, subsist, dwell, abide, reside.
Lively - active, energetic, brisk, nimble, jocund, merry, sprightly, vigorous. Lodge - accommodate, entertain, shelter harbor. Loftiness - height, haughtiness, stateliness, elevation, dignity, pride. Loiter - lag, saunter, linger.
Lonely - dreary, lonesome, retired, solitary.
Look - see, behold, view, inspect, appearance.
Loose - unconnected, open, unrestrained, dissolute, licentious, unjointed.
Loss - injury, damage, detriment, waste.
Lot - share, portion, fate, fortune, destiny.
Loud - noisy, vociferous, clamorous, turbulent, vehement.
Love - liking, affection, fondness, kindness, attachment, adoration, esteem.
Lovely - attractive, amiable, elegant, charming, handsome, fine, delightful, beautiful.
Lover-beau, wooer, suitor.
Loving - kind, affectionate, attentive, tender, amorous.
Low - humble, mean, base, abject, debased, dejected, despicable.
Lower - humble, humiliate, debase, degrade.
Lucky - successful, fortunate, prosperous.
Ludicrous - amusing, comical, droll, laughable.
Lunacy - mania, derangement, insanity, madness.
Luxuriant - excessive, voluptuous, abundant, exuberant.
Luxury - profusion, abundance, excess.
Magnificent - noble, grand, sublime, glorious, splendid, superb.