if, or: Do not say “seldom or ever,” say, rather, “seldom if ever,” or “seldom or never.”
if, whether: Sometimes if is incorrectly used for whether. It is used correctly when supposition or condition is implied; whether, chiefly when an alternative is suggested or presented. “If he sends the money I shall then decide whether or not I will go.”
ill: The Standard Dictionary says: The use of ill and sick differs in the two great English-speaking countries. Ill is used in both lands alike, but the preferred sense of sick in England is that of “sick at the stomach, nauseated,” while in the United States the two words are freely interchangeable. Still Tennyson and other good writers freely use sick in the sense of ill. The tendency of modern usage is to remand ill and well (referring to condition of health) to the predicate. We say “A person who is ill,” rather than “An ill person”; “I am well,” but not “I am in a well state of health.” Ill in the abstract sense of bad or wicked is obsolescent, or rather practically obsolete except in poetic or local use. Compare [ILLY].
illusion. Compare [DELUSION].
illy: This word should never be used for ill since ill is both an adverb and an adjective. Say, “He behaved ill”; not “he behaved illy.” Illy is now obsolescent.
immerge. Compare [EMERGE].
immigrant. Compare [EMIGRANT].
imminent. Compare [EMINENT].
immunity and impunity are sometimes confounded. They are both from the Latin, the former being produced by in, not, + munus, service, and the latter by in + pœna, punishment. Freedom from any burden, or exemption from evil, duty or penalty has perhaps not unnaturally, been associated with freedom from punishment. A boy may insult his brother with impunity but can not expect to enjoy a like immunity from strangers.
impending. Compare [EMINENT].