waterfall vs falls

waterfall and falls both are nouns.

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

As nouns, waterfall and falls are synonyms defined as:

waterfall (noun)	falls (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)