Definition of いっしょう
- (n-adv, n-t, adj-no) whole life; a lifetime; all through life; one existence; a generation; an age; the whole world; the era
あなたは、一生勉強しなければならない。
You must study your whole life. - (adj-no) (the only, the greatest, etc.) of one's life
マイホームは一生の買い物だからね、そんな即断即決はできないよ。
A home is a once-in-a-lifetime purchase so you don't want to make any snap decisions.