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The definition of lifetime

3 Definitions of: lifetime

1. noun, a) the length of time a person or animal is alive b) (as modifier)
2. noun, the length of time that something functions, is useful, etc
3. noun, physics the average time of existence of an unstable or reactive entity, such as a nucleus, excited state, elementary particle, etc; mean life
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5. Show me the etymology of the word: lifetime

Synonyms:	time, existence, course, period, span, life span

From Collins