calm down vs tranquillise

calm down and tranquillise both are verbs.

Word	Noun	Adjective	Verb	Adverb
calm down	No	No	Yes	No
tranquillise	No	No	Yes	No

As verbs, calm down and tranquillise are synonyms defined as:

Other synonyms of calm down include calm, lull, quiet, quieten, still, tranquilize, tranquillize.

calm down (verb)	tranquillise (verb)
become quiet or less intensive	cause to be calm or quiet as by administering a sedative to
make calm or still	make calm or still
become quiet or calm, especially after a state of agitation