tranquilliser vs tranquillizer

tranquilliser and tranquillizer both are nouns.

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

As nouns, tranquilliser and tranquillizer are synonyms defined as:

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

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

tranquilliser (noun)	tranquillizer (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