1.
taboo, something forbidden, something to avoid
Something that should be avoided or refrained from in a particular situation. Often used in the pattern ~は禁物 (... is something to be avoided) to warn against certain behaviors or actions.
Usage
Almost always appears in the pattern ~は禁物だ, functioning as a warning or advice that something should be avoided. This is an idiomatic expression rather than a word used freely in various grammatical constructions.