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lifetime

[lahyf-tahym]
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noun
  1. the time that the life of someone or something continues; the term of a life: peace within our lifetime.
  2. Physics. mean life.
adjective
  1. for the duration of a person's life: He has a lifetime membership in the organization.

Origin of lifetime

First recorded in 1175–1225, lifetime is from the Middle English word liftime. See life, time
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for lifetime

lifetime

noun
    1. the length of time a person or animal is alive
    2. (as modifier)a lifetime supply
  1. the length of time that something functions, is useful, etc
  2. physics the average time of existence of an unstable or reactive entity, such as a nucleus, excited state, elementary particle, etc; mean life
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for lifetime

n.

also life-time, early 13c., from life (n.) + time (n.). One word from 19c. Old English had lifdæg in same sense, literally "life day."

Online Etymology Dictionary, © 2010 Douglas Harper

lifetime in Medicine

lifetime

(līftīm′)
n.
  1. The period of time during which an individual is alive.
  2. The period of time during which property, an object, a process, or a phenomenon exists or functions.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.