decubitus ulcer vs ulcer

decubitus ulcer and ulcer both are nouns.

Word	Noun	Adjective	Verb	Adverb
decubitus ulcer	Yes	No	No	No
ulcer	Yes	No	No	No

As nouns, ulcer is a hypernym of decubitus ulcer; that is, ulcer is a word with a broader meaning than decubitus ulcer:

decubitus ulcer: a chronic ulcer of the skin caused by prolonged pressure on it (as in bedridden patients)
ulcer: a circumscribed inflammatory and often suppurating lesion on the skin or an internal mucous surface resulting in necrosis of tissue

Other hypernyms of decubitus ulcer include ulceration.

decubitus ulcer (noun)	ulcer (noun)
a chronic ulcer of the skin caused by prolonged pressure on it (as in bedridden patients)	a circumscribed inflammatory and often suppurating lesion on the skin or an internal mucous surface resulting in necrosis of tissue