windfall vs gold rush

windfall and gold rush both are nouns.

Word	Noun	Adjective	Verb	Adverb
windfall	Yes	No	No	No
gold rush	Yes	No	No	No

As nouns, windfall and gold rush are synonyms defined as:

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

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

windfall (noun)	gold rush (noun)
a sudden happening that brings good fortune (as a sudden opportunity to make money)	a large migration of people to a newly discovered gold field
fruit that has fallen from the tree	a sudden happening that brings good fortune (as a sudden opportunity to make money)