coffeecake vs coffee cake

coffeecake and coffee cake both are nouns.

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

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

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

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