life ‧ time /ˈlaɪftaɪm/ BrE AmE noun [countable usually singular]
1 . the period of time during which someone is alive or something exists ⇨ lifespan
during/in sb’s lifetime
During her lifetime she had witnessed two world wars.
It’s the sort of opportunity you see only once in a lifetime.
2 . the chance/experience etc of a lifetime the best opportunity, experience etc that you will ever have:
It was the holiday of a lifetime.
3 . not in this lifetime spoken not at all SYN never :
‘Would you go out with him after he dropped you?’ ‘Not in this lifetime.’