INTRIGUE—plot, cabal, conspiracy, combination, artifice, ruse, amour.
INTRINSIC—real, true, genuine, sterling, native, natural. (Extrinsic.)
INVALIDATE—quash, cancel, overthrow, vacate, nullify, annul.
INVASION—incursion, irruption, inroad, aggression, raid, fray.
INVECTIVE—abuse, reproach, railing, censure, sarcasm, satire.
INVENT—devise, contrive, frame, find out, discover.
INVESTIGATION—examination, search, inquiry, research, scrutiny.
INVETERATE—confirmed, chronic, malignant. (Inchoate.)
INVIDIOUS—envious, hateful, odious, malignant.
INVIGORATE—brace, harden, nerve, strengthen, fortify. (Enervate.)