insurer vs insurance company

insurer and insurance company both are nouns.

Word	Noun	Adjective	Verb	Adverb
insurer	Yes	No	No	No
insurance company	Yes	No	No	No

As nouns, insurer and insurance company are synonyms defined as:

insurer and insurance company: a financial institution that sells insurance

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

insurer (noun)	insurance company (noun)
a financial institution that sells insurance	a financial institution that sells insurance