adverb
all; entirely; completely; without exception
Adverbial form of 残す (to leave behind), meaning 'without leaving anything behind' → 'all, entirely'. Often used with verbs like 食べる, 使う, 話す to emphasize completeness.
See also: 残らず
料理を残さず食べた。
I ate all of the food without leaving any.
彼は自分の考えを残さず話した。
He spoke his thoughts completely, without holding anything back.