ice cap vs ice mass

ice cap and ice mass both are nouns.

Word	Noun	Adjective	Verb	Adverb
ice cap	Yes	No	No	No
ice mass	Yes	No	No	No

As nouns, ice mass is a hypernym of ice cap; that is, ice mass is a word with a broader meaning than ice cap:

ice cap: a mass of ice and snow that permanently covers a large area of land (e.g., the polar regions or a mountain peak)
ice mass: a large mass of ice

ice cap (noun)	ice mass (noun)
a mass of ice and snow that permanently covers a large area of land (e.g., the polar regions or a mountain peak)	a large mass of ice