policyholder vs customer

policyholder and customer both are nouns.

Word	Noun	Adjective	Verb	Adverb
policyholder	Yes	No	No	No
customer	Yes	No	No	No

As nouns, customer is a hypernym of policyholder; that is, customer is a word with a broader meaning than policyholder:

policyholder: a person who holds an insurance policy; usually, the client in whose name an insurance policy is written
customer: someone who pays for goods or services

Other hypernyms of policyholder include client, holder.

policyholder (noun)	customer (noun)
a person who holds an insurance policy; usually, the client in whose name an insurance policy is written	someone who pays for goods or services