underwriter vs insurer

underwriter and insurer both are nouns.

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

As nouns, underwriter and insurer are synonyms defined as:

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

underwriter (noun)	insurer (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