I. ˈlīf-ˌtīm noun
Date: 13th century
1.
a. : the duration of the existence of a living being (as a person or an animal) or a thing (as a star or a subatomic particle)
b. : life 12
2. : an amount accumulated or experienced in a lifetime
a lifetime of regrets
II. adjective
Date: 1834
1. : lifelong
2. : of long duration or continuance
lifetime legislation
3. : measured or achieved over the span of a career
a baseball player's lifetime batting average