expression
without saying a word
Set phrase meaning completely silent, not uttering a single word. Often used in narrative or descriptive contexts.
彼は一言も言わずに部屋を出て行った。
He left the room without saying a word.
一言も言わずにうなずいた。
She nodded without saying a word.
黙って is a more general 'silently' or 'without speaking', while 一言も言わず emphasizes not even a single word was spoken.
Compound of 一言 (ひとこと, 'a single word') + も (inclusive particle) + 言わず (negative continuative of 言う, 'to say'). The phrase literally means 'not saying even one word'.