Orion vs diffuse nebula

Orion and diffuse nebula both are nouns.

Word	Noun	Adjective	Verb	Adverb
Orion	Yes	No	No	No
diffuse nebula	Yes	No	No	No

As nouns, diffuse nebula is a hypernym of Orion; that is, diffuse nebula is a word with a broader meaning than Orion:

Orion: a constellation on the equator to the east of Taurus; contains Betelgeuse and Rigel
diffuse nebula: a cluster of stars within an intricate cloud of gas and dust

Other hypernyms of Orion include gaseous nebula.

Orion (noun)	diffuse nebula (noun)
a constellation on the equator to the east of Taurus; contains Betelgeuse and Rigel	a cluster of stars within an intricate cloud of gas and dust
(Greek mythology) a giant Boeotian hunter who pursued the Pleiades and was eventually slain by Artemis; was then placed in the sky as a constellation