diffuse nebula vs Orion

diffuse nebula and Orion both are nouns.

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

As nouns, Orion is a hyponym of diffuse nebula; that is, Orion is a word with a more specific, narrower meaning than diffuse nebula:

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

Other hyponyms of diffuse nebula include Hunter.

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