also: いちごんせっく
noun
every single word and phrase; each and every word
Emphasizes that every single word or phrase is included, without exception. Often used in formal or literary contexts.
彼の演説は一言隻句も聞き漏らせないほど重要だった。
His speech was so important that I couldn't afford to miss a single word.
契約書の一言隻句にも注意を払う必要がある。
You need to pay attention to every single word and phrase in the contract.
一言一句 is a more common synonym with the same meaning, used in both formal and everyday contexts.
Compound of 一言 (one word) and 隻句 (a single phrase), where 隻 is a counter for one of a pair, emphasizing the smallest unit of speech.