ice cap vs icecap

ice cap and icecap both are nouns.

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

As nouns, ice cap and icecap are synonyms defined as:

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

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