nebula vs nebulous

nebula is a noun but nebulous is not a noun.

Word	Noun	Adjective	Verb	Adverb
nebula	Yes	No	No	No
nebulous	No	Yes	No	No

nebula (noun)	nebulous (noun)
(pathology) a faint cloudy spot on the cornea
an immense cloud of gas (mainly hydrogen) and dust in interstellar space
cloudiness of the urine
a medicinal liquid preparation intended for use in an atomizer

nebula (adjective)	nebulous (adjective)
	of or relating to or resembling a nebula
	lacking definition or definite content
	lacking definite form or limits