windfall vs bonanza

windfall and bonanza both are nouns.

Word	Noun	Adjective	Verb	Adverb
windfall	Yes	No	No	No
bonanza	Yes	No	No	No

As nouns, windfall and bonanza are synonyms defined as:

windfall and bonanza: a sudden happening that brings good fortune (as a sudden opportunity to make money)

Other synonyms of windfall include boom, bunce, godsend, gold rush, gravy, manna from heaven.

windfall (noun)	bonanza (noun)
a sudden happening that brings good fortune (as a sudden opportunity to make money)	a sudden happening that brings good fortune (as a sudden opportunity to make money)
fruit that has fallen from the tree	an especially rich vein of precious ore