ice mass vs floe

ice mass and floe both are nouns.

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

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

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

ice mass (noun)	floe (noun)
a large mass of ice	a flat mass of ice (smaller than an ice field) floating at sea