Idiotic means completely, maddeningly brainless. A decision nobody sensible would have made.
It is an insult and a fairly hot one, and it attaches to ideas, rules and behaviour more comfortably than to people. Like moron and imbecile, the noun idiot began as a medical classification, which is worth knowing even though idiot has drifted far enough from that history to be the mildest of the three now. Stupid and foolish are the plainer alternatives and daft is the affectionate British one.
1adjectiveidioticExtremely foolish or senseless.
“It was an idiotic thing to attempt in that weather.”
Also accepted in games: stupid, foolish
Middle English
ydiote
English
idiot
English, today
idiotic
Built from
From idiot + -ic. idiot comes from Middle English ydiote. From Middle English idiote, ydiote, from Old French idiote (later idiot), from Latin idiota, from Ancient Greek ἰδιώτης (“a private citizen, one who has no professional knowledge, layman”), from ἴδιος (“one's own, pertaining to oneself, private”). a doublet of idiota. by surface analysis, idi- + -ot.
Etymology from Wiktionary, CC BY-SA