tranquillizer - definition and synonyms

noun [countable] 

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/ˈtræŋkwɪlaɪzə(r)/
singulartranquillizer
pluraltranquillizers
  1. a drug that makes people calmer when they are very worried or nervous
    be on tranquillizers (=take them regularly):

    She’s been on tranquillizers ever since the accident.