free time
Synonym discussion
Sense: noun/1
All four words point to hours away from work or duty, but they differ in tone and focus. 'Free time' is the everyday, neutral term — it simply names the hours you can fill as you like, whether you rest or stay busy. 'Spare time' overlaps almost completely, though it hints at time left over once the necessary things are done. 'Leisure' is more formal and stresses relaxation and pleasure, so it suits writing about hobbies, travel, or culture. 'Downtime' is informal and originally described machines that stopped running; for people it means a break to recover and recharge. For example, you might say 'I read in my free time', 'I fixed the gate in my spare time', and 'the resort is built for total leisure', but 'the team needs downtime after the busy season'.
Etymology
A transparent compound of the adjective 'free' and the noun 'time'. 'Free' comes from Old English 'frēo', meaning not enslaved or not bound, which later widened to mean 'not occupied' or 'available'. Joined with 'time', it names the time that is not claimed by work or duty — a fairly modern fixed phrase that grew common as the idea of regular leisure spread.