three-toed sloth vs tree sloth

three-toed sloth and tree sloth both are nouns.

Word	Noun	Adjective	Verb	Adverb
three-toed sloth	Yes	No	No	No
tree sloth	Yes	No	No	No

As nouns, tree sloth is a hypernym of three-toed sloth; that is, tree sloth is a word with a broader meaning than three-toed sloth:

three-toed sloth: a sloth that has three long claws on each forefoot and each hindfoot
tree sloth: any of several slow-moving arboreal mammals of South America and Central America; they hang from branches back downward and feed on leaves and fruits

Other hypernyms of three-toed sloth include sloth.

three-toed sloth (noun)	tree sloth (noun)
a sloth that has three long claws on each forefoot and each hindfoot	any of several slow-moving arboreal mammals of South America and Central America; they hang from branches back downward and feed on leaves and fruits