chain saw vs chainsaw

chain saw and chainsaw both are nouns.

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

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

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

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