something that makes something unpleasant less strong or less unpleasant

a pain/stress reliever 止疼药/缓解压力的事

a reliever of boredom 消除无聊情绪的事

a drug used to treat acute (= sudden and bad) asthma (= a condition that makes breathing difficult)

Relievers work rapidly to open up airways and help breathing. 扩张剂能迅速打开气道，帮助呼吸。|确保您的孩子知道一定要随身带着支气管扩张剂吸入器。

Make sure your child knows to have their reliever inhaler with them at all times. 确保你的孩子知道要一直带着他们的缓解药物吸入器。

in baseball, a pitcher (= a player who throws the ball to the player with the bat) who comes on to play instead of another pitcher

He pitched in 45 games, mostly as a reliever. 他作为投手参加了45场比赛，主要都是作为中继投手上场的。