tranquillize
Concise Oxford English Dictionary © 2008 Oxford University Press:
tranquillize /ˈtraŋkwəlʌɪz/ (or tranquillise; US tranquilize)
▶verb (usu. as adj. tranquillizing) (especially of a drug) have a calming or sedative effect on.
■ administer a tranquillizing drug to.
– derivatives
tranquillizer noun.
tranquillizer noun.
'tranquillize' also found in these Oxford entries:

