tranquillizer vs tranquilliser

tranquillizer and tranquilliser both are nouns.

Word	Noun	Adjective	Verb	Adverb
tranquillizer	Yes	No	No	No
tranquilliser	Yes	No	No	No

As nouns, tranquillizer and tranquilliser are synonyms defined as:

tranquillizer and tranquilliser: a drug used to reduce stress or tension without reducing mental clarity

Other synonyms of tranquillizer include antianxiety agent, ataractic, ataractic agent, ataractic drug, tranquilizer.

tranquillizer (noun)	tranquilliser (noun)
a drug used to reduce stress or tension without reducing mental clarity	a drug used to reduce stress or tension without reducing mental clarity