also: いちげんはんく
noun
a single word; even a word; even a syllable
Used in negative contexts to emphasize that not even a single word or syllable is spoken, written, or revealed. Often appears in set phrases like 一言半句も～ない.
彼はそのことについて一言半句も話さなかった。
He didn't say a single word about it.
秘密を一言半句も漏らしてはいけない。
You must not leak even a syllable of the secret.
一言 is a common word for 'a single word' or 'a brief remark', used in both positive and negative contexts. 一言半句 is a stronger, more emphatic yojijukugo used almost exclusively in negative constructions.
A yojijukugo composed of 一言 (one word) and 半句 (half a phrase), together emphasizing the smallest unit of speech. The exact origin is uncertain, but it follows a common pattern of intensifying through repetition of similar concepts.