a single word; (not even) a word or syllable
Used in negative contexts to emphasize that not even a single word or syllable is spoken, written, or changed. Often appears in set phrases like 一字半句も～ない.
He didn't utter a single word of complaint.
We couldn't change even a single word of the contract.
Compound of 一字 (one character/word) and 半句 (half a phrase), emphasizing a minimal unit of language. The exact historical derivation is uncertain.