1. the duration of a person's life: "a reward for a lifetime's work"Similarlifespanlifedaysduration of lifeallotted spancourse of lifetime on earthexistenceone's timeone's careerone's threescore years and tenthis mortal coilinformal:one's born days
▪ the duration of a thing's existence or usefulness: "a plan to extend the lifetime of satellites"Similardurationlifeactive lifeexistencelife expectancyfunctioning periodperiod of effectiveness/usefulness/validity/efficacy
▪ used to express the view that a period is very long:"five weeks was a lifetime, and anything could have happened"Similarall one's lifea very long timean eternityhoursdaysmonthsyearseonshours/days/months on endinformal:ages (and ages)an age