prickly pear cactus vs cactus

prickly pear cactus and cactus both are nouns.

Word	Noun	Adjective	Verb	Adverb
prickly pear cactus	Yes	No	No	No
cactus	Yes	No	No	No

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

prickly pear cactus: cacti having spiny flat joints and oval fruit that is edible in some species; often used as food for stock
cactus: any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines

prickly pear cactus (noun)	cactus (noun)
cacti having spiny flat joints and oval fruit that is edible in some species; often used as food for stock	any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines