specialist vs specializer

specialist and specializer both are nouns.

Word	Noun	Adjective	Verb	Adverb
specialist	Yes	No	No	No
specializer	Yes	No	No	No

As nouns, specialist and specializer are synonyms defined as:

specialist and specializer: an expert who is devoted to one occupation or branch of learning

Other synonyms of specialist include specialiser.

specialist (noun)	specializer (noun)
an expert who is devoted to one occupation or branch of learning	an expert who is devoted to one occupation or branch of learning
practices one branch of medicine