n.

1. （有时与代词的所有格连用）一生，终身；（事物的）使用期，寿命[S]
   He has gone through many a severe test during his lifetime.

   他一生中经受过多次严峻的考验。

   She devoted her lifetime to the study of zoology.

   她以毕生精力从事动物学研究。

a.

1. 一生的，终身的
   the lifetime employment system

   终身雇佣制

n.

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