tranquillize

 
Pronunciation: /ˈtraŋkwɪlʌɪz/
(also tranquillise; US tranquilize)

verb

[with object] (usually as adjective tranquillizing)
  • (of a drug) have a calming or sedative effect on: the majority regarded tranquillizing drugs as the chief therapeutic weapon
  • administer a tranquillizer to (a person or animal): the dogs had to be tranquillized before their owner’s body could be brought out
  • literary make tranquil: joys that tranquillize the mind

Spelling help

Remember that tranquillize is spelled with a double l (the spelling tranquilize is American).