Nautiterm: (Nautical Terms Explained) – “idle/idler”

Idler was the name for the members of a ship’s crew which did not join in with night watch because of their work. Carpenters, sailmakers, cooks, etc worked during the day, and were excused from watch duty at night. They were called idlers, but not because they had nothing to do, simply because they were off duty at night.