falls vs waterfall

falls and waterfall both are nouns.

Word	Noun	Adjective	Verb	Adverb
falls	Yes	No	No	No
waterfall	Yes	No	No	No

As nouns, falls and waterfall are synonyms defined as:

falls (noun)	waterfall (noun)
a steep descent of the water of a river	a steep descent of the water of a river
the petals or sepals of a flower that bend downward (especially the outer perianth of an iris)