Ad hominem
Etymology
Latin "ad hominem" means "to the person," short for "argumentum ad hominem." In older logic the phrase named a legitimate move — arguing from an opponent’s own stated commitments — but by the twentieth century it hardened into its modern sense of a personal attack. The shift means the label now flags a discrediting swipe rather than Locke’s narrower technical device.
noun phrase · /ad-HOM-ih-nem/
Attacking the person making an argument rather than the argument itself.
What it names
Spotting it keeps a debate about the claim on the table instead of about the character of whoever raised it.
Example
Rather than answer the cost estimate, she said only that its author had flunked economics — a textbook ad hominem.
Related idea
A tu quoque is a specific ad hominem that answers criticism with "you do it too" instead of engaging.