Opuntia tuna vs prickly pear

Opuntia tuna and prickly pear both are nouns.

Word	Noun	Adjective	Verb	Adverb
Opuntia tuna	Yes	No	No	No
prickly pear	Yes	No	No	No

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

Opuntia tuna: tropical American prickly pear of Jamaica
prickly pear: cacti having spiny flat joints and oval fruit that is edible in some species; often used as food for stock

Other hypernyms of Opuntia tuna include prickly pear cactus.

Opuntia tuna (noun)	prickly pear (noun)
tropical American prickly pear of Jamaica	round or pear-shaped spiny fruit of any of various prickly pear cacti
	cacti having spiny flat joints and oval fruit that is edible in some species; often used as food for stock