chainsaw vs chain saw

chainsaw and chain saw both are nouns.

Word	Noun	Adjective	Verb	Adverb
chainsaw	Yes	No	No	No
chain saw	Yes	No	No	No

As nouns, chainsaw and chain saw are synonyms defined as:

chainsaw and chain saw: portable power saw; teeth linked to form an endless chain

chainsaw (noun)	chain saw (noun)
portable power saw; teeth linked to form an endless chain	portable power saw; teeth linked to form an endless chain