spiral nebula vs spiral galaxy

spiral nebula and spiral galaxy both are nouns.

Word	Noun	Adjective	Verb	Adverb
spiral nebula	Yes	No	No	No
spiral galaxy	Yes	No	No	No

As nouns, spiral nebula and spiral galaxy are synonyms defined as:

spiral nebula and spiral galaxy: a galaxy having a spiral structure; arms containing younger stars spiral out from old stars at the center

spiral nebula (noun)	spiral galaxy (noun)
a galaxy having a spiral structure; arms containing younger stars spiral out from old stars at the center	a galaxy having a spiral structure; arms containing younger stars spiral out from old stars at the center