n.

1. （有時與代名詞的所有格連用）一生，終身；（事物的）使用期，壽命[S]
   He has gone through many a severe test during his lifetime.

   他一生中經受過多次嚴峻的考驗。

   She devoted her lifetime to the study of zoology.

   她以畢生精力從事動物學研究。

a.

1. 一生的，終身的
   the lifetime employment system

   終身僱傭制

n.

1. the duration of a person's life or of a thing's existence or usefulness.
2. informal a very long time.