休息

It covers everything from a five-minute pause (休息一下, 'take a short break') to a full day off. As a verb, it works without an object: 我要休息 ('I need to rest'). It can also act as a noun for 'a break': 课间休息 ('class break / recess').

Two cultural notes: in offices and schools, 午休 (wǔxiū, 'midday rest') is the institutionalized lunchtime nap, often 30-90 minutes; and Chinese signs on closed shops typically read 休息 ('closed for break / day off'). The phrase 好好休息 (hǎohǎo xiūxi) — literally 'rest well' — is the standard way to wish someone recovery when they're tired or sick, equivalent to 'get some rest.' The opposite is 工作 (gōngzuò, 'to work').