Leisure comes from Latin licēre meaning 'to be permitted'. It originally meant not rest but permission — the freedom to do as you please. The same root gives us licence and illicit.
Free time; time when one is not working or occupied; unhurried ease.
From Old French leisir meaning 'permission, ability, leisure, free time', from Latin licēre meaning 'to be permitted, to be allowed'. Leisure is, at its root, not rest but permission — the state of being allowed to do as you please. The Latin licēre also gives us licence (permission to act), licit (permitted), and illicit (not permitted). The shift from 'permission' to 'free time' happened in Old French: having permission implied having the freedom
Leisure and illicit are cousins from the same Latin root. Licēre meant 'to be permitted'. Leisure is the state of having permission to do as you please. Illicit is the state of not having permission at all. One implies relaxation; the other, crime. The same permission separates a holiday from a heist.