insurer vs underwriter

insurer and underwriter both are nouns.

Word	Noun	Adjective	Verb	Adverb
insurer	Yes	No	No	No
underwriter	Yes	No	No	No

As nouns, insurer and underwriter are synonyms defined as:

Other synonyms of insurer include insurance company, insurance firm, insurance underwriter.

insurer (noun)	underwriter (noun)
a financial institution that sells insurance	a financial institution that sells insurance
	a banker who deals chiefly in underwriting new securities
	an agent who sells insurance