tranquilliser

/T R AE0 NG K W IH1 L AY0 Z ER0/
noun
  1. 1

    That which tranquillizes or soothes.

  2. 2

    A drug used to reduce anxiety or tension; a sedative.

Source: https://en.wiktionary.org/wiki/tranquilizer, https://en.wiktionary.org/wiki/tranquilliser