Formal/literary. The most recognizable use in modern Chinese is the historical-drama line 皇上息怒 (Your Majesty, calm your anger), kneeling minister optional. In everyday speech you'd say 别生气了 (bié shēngqì le).
memory
息 (rest, extinguish) + 怒 (anger) — literally 'extinguish the anger.' Same 息 is in 休息 (xiūxi, rest) and 平息 (píngxī, quell).
