Opuntia cholla vs cactus

Opuntia cholla and cactus both are nouns.

Word	Noun	Adjective	Verb	Adverb
Opuntia cholla	Yes	No	No	No
cactus	Yes	No	No	No

As nouns, cactus is a hypernym of Opuntia cholla; that is, cactus is a word with a broader meaning than Opuntia cholla:

Opuntia cholla: arborescent cacti having very spiny cylindrical stem segments; southwestern United States and Mexico
cactus: any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines

Opuntia cholla (noun)	cactus (noun)
arborescent cacti having very spiny cylindrical stem segments; southwestern United States and Mexico	any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines