tranquillizerPronunciation: /ˈtraŋkwɪlʌɪzə/ (also tranquilliser; US also tranquilizer)Translate tranquillizer | into French | into German | into Italian | into Spanish Definition of tranquillizer noun a medicinal drug taken to reduce tension or anxiety. tranquillizer in other Oxford dictionaries Definition of tranquillizer in the US English dictionary