'lifetime' originates from the combination of 'life' and 'time', where 'life' meant 'the condition that distinguishes animals and plants from inorganic matter' and 'time' referred to 'the indefinite continued progress of existence'.

'lifetime' evolved from the Old English word 'līf' meaning 'life' and 'tīma' meaning 'time', eventually forming the modern English word 'lifetime'.

Initially, it meant 'the duration of a person's life', and this meaning has largely remained the same in modern usage.