ice mass vs ice cap

ice mass and ice cap both are nouns.

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

As nouns, ice cap is a hyponym of ice mass; that is, ice cap is a word with a more specific, narrower meaning than ice mass:

ice mass: a large mass of ice
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)

Other hyponyms of ice mass include glacier, berg, iceberg, icecap, ice field, floe, ice floe.

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