coffee cake vs coffeecake

coffee cake and coffeecake both are nouns.

Word	Noun	Adjective	Verb	Adverb
coffee cake	Yes	No	No	No
coffeecake	Yes	No	No	No

As nouns, coffee cake and coffeecake are synonyms defined as:

coffee cake and coffeecake: a cake or sweet bread usually served with coffee

coffee cake (noun)	coffeecake (noun)
a cake or sweet bread usually served with coffee	a cake or sweet bread usually served with coffee