Antiphrasis

Antiphrasis is the figure by which a word is used to mean the opposite of what it ordinarily denotes. The classic case is the ironic epithet: a bald man nicknamed 'Curly', a huge dog named 'Tiny', a bitter drink advertised as 'the friendly bitters'. Because the ordinary meaning is so plainly wrong, the reader supplies the intended meaning and — usually — smiles.

The figure is a species of irony, but a narrower one: irony can operate over whole sentences and situations, while antiphrasis operates on a single word. Classical rhetoricians treated it as a distinct trope precisely because the mechanism is so compact — a one-word inversion, licensed by shared knowledge between speaker and audience.

It is common in nicknames, in mock-formal titles ('His Excellency the Cat'), and in euphemistic naming ('the Kindly Ones' for the Furies, in Greek). In each case the substitution both softens and sharpens: it avoids naming the frightening thing while pointing at it more sharply than the plain name would.

Common mistake: using antiphrasis where the audience cannot share the reference. The figure fails silently: a reader who does not know that the vast bouncer is called 'Tiny' takes the sentence at face value and misses both the joke and the character-note it was doing.