丢失 (diū shī) is a formal or literary verb meaning 'to lose'—typically referring to misplacing or no longer having possession of something, especially in writing, official contexts, or when emphasizing the abstract sense of loss. It combines 丢 (diū), which means 'to throw away' or 'to discard', and 失 (shī), meaning 'to lose' or 'to miss'. Together, they intensify the idea of irreversible or significant loss—not just physical absence but often implying negligence, accident, or consequence.

This word is commonly used for lost documents, data, opportunities, or personal items in formal reports, news, or administrative language. It’s less common in casual speech (where people prefer 丢了, the colloquial contraction) and rarely used for living beings—never for people or pets (use 走失 instead). It can also appear in compound nouns like 丢失率 (loss rate) or 数据丢失 (data loss).