dorsal vs dorsum

dorsal is not a noun while dorsum is a noun.

Word	Noun	Adjective	Verb	Adverb
dorsal	No	Yes	No	No
dorsum	Yes	No	No	No

dorsal (noun)	dorsum (noun)
	the back of the body of a vertebrate or any analogous surface (as the upper or outer surface of an organ or appendage or part)
	the posterior part of a human (or animal) body from the neck to the end of the spine

dorsal (adjective)	dorsum (adjective)
belonging to or on or near the back or upper surface of an animal or organ or part
facing away from the axis of an organ or organism