gold rush vs migration

gold rush and migration both are nouns.

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

As nouns, migration is a hypernym of gold rush; that is, migration is a word with a broader meaning than gold rush:

gold rush (noun)	migration (noun)
a large migration of people to a newly discovered gold field	the movement of persons from one country or locality to another
a sudden happening that brings good fortune (as a sudden opportunity to make money)	the periodic passage of groups of animals (especially birds or fishes) from one region to another for feeding or breeding
	(chemistry) the nonrandom movement of an atom or radical from one place to another within a molecule
	a group of people migrating together (especially in some given time period)