Words That Now Mean the Opposite of What They Meant

Semantic drift is constant and mostly invisible, because it happens slower than a lifetime. But some words have travelled far enough that the original meaning is unrecognisable.

The finished reversals

Nice — from Latin nescius, ignorant. It meant foolish, then fussy, then precise (a sense surviving in a nice distinction), and finally pleasant.
Awful — full of awe. The Bible describes God as awful, meaning majestic.
Silly — from Old English gesælig, blessed, then innocent, then simple, then foolish.
Naughty — having nothing, poor. Then wicked, now mildly disobedient.
Terrific — causing terror. Now excellent.
Egregious — standing out from the flock, so distinguished. Now outstandingly bad.
Sophisticated — adulterated, corrupted. Now refined.
Artificial — made with skill, hence admirable. Now the opposite of natural.

Nobody argues about these. The reversal is complete, so the old meaning has no defenders left.

The reversals in progress

These are the ones that produce arguments, because both meanings are live and people were taught different ones.

Decimate. Originally a Roman military punishment: kill one man in ten. So it meant reduce by a tenth. It now means destroy most of, which is close to the reverse. Both are in dictionaries; the older sense is effectively dead in ordinary use, and insisting on it makes sentences harder to read rather than more precise.

Peruse. Meant to read thoroughly and carefully. Now widely used to mean skim. Dictionaries record both, and the two are direct opposites — which makes the word genuinely unusable in careful writing. If you mean skim, write skim.

Nonplussed. Meant bewildered, at a loss. In American usage it has drifted towards unbothered, again close to the opposite. Same problem: the word can no longer be relied on to communicate.

Enormity. Traditionally meant great wickedness, not great size. The enormity of the task is now common and still objected to. Enormousness is the traditional alternative and is an ugly word, which is part of why the drift is winning.

Bemused. Means confused. Frequently used to mean mildly amused, presumably by association with amused.

The practical rule

When a word is mid-reversal, it has stopped working, and that is the actual problem — not that one side is wrong.

If half your readers understand nonplussed as bewildered and half as unbothered, the sentence communicates nothing reliable no matter which you intended. The fix is not to pick the correct meaning and stand firm. It is to use a different word.

Instead of peruse: read closely or skim.
Instead of nonplussed: baffled or unfazed.
Instead of enormity: scale, or wickedness.
Instead of bemused: puzzled or wry.

Every replacement is clearer, and none of them requires you to be right about the history.

Why words drift towards the negative

Notice how many of these got worse rather than better: silly, naughty, egregious, notorious, vulgar (once simply common).

Linguists call this pejoration, and it is more common than the reverse. The usual explanation is that words used sarcastically or euphemistically eventually absorb the tone they were being used against — which is why every polite term for an unpleasant thing eventually becomes an unpleasant term and has to be replaced.