bark vs cassia bark

bark and cassia bark both are nouns.

Word	Noun	Adjective	Verb	Adverb
bark	Yes	No	Yes	No
cassia bark	Yes	No	No	No

As nouns, cassia bark is a hyponym of bark; that is, cassia bark is a word with a more specific, narrower meaning than bark:

bark: tough protective covering of the woody stems and roots of trees and other woody plants
cassia bark: aromatic bark of the cassia-bark tree; less desirable as a spice than Ceylon cinnamon bark

bark (noun)	cassia bark (noun)
a sailing ship with 3 (or more) masts	aromatic bark of the cassia-bark tree; less desirable as a spice than Ceylon cinnamon bark
the sound made by a dog
a noise resembling the bark of a dog
tough protective covering of the woody stems and roots of trees and other woody plants