thunderhead vs cumulus

thunderhead and cumulus both are nouns.

Word	Noun	Adjective	Verb	Adverb
thunderhead	Yes	No	No	No
cumulus	Yes	Yes	No	No

As nouns, cumulus is a hypernym of thunderhead; that is, cumulus is a word with a broader meaning than thunderhead:

thunderhead: a rounded projecting mass of a cumulus cloud with shining edges; often appears before a thunderstorm
cumulus: a globular cloud

Other hypernyms of thunderhead include cumulus cloud.

thunderhead (noun)	cumulus (noun)
a rounded projecting mass of a cumulus cloud with shining edges; often appears before a thunderstorm	a collection of objects laid on top of each other
	a globular cloud

thunderhead (adjective)	cumulus (adjective)
	of or related to cumulous clouds