nebula vs fleck

nebula and fleck both are nouns.

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

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

Other hypernyms of nebula include dapple, maculation, patch, speckle, spot.

nebula (noun)	fleck (noun)
(pathology) a faint cloudy spot on the cornea	a small contrasting part of something
an immense cloud of gas (mainly hydrogen) and dust in interstellar space	a small fragment of something broken off from the whole
cloudiness of the urine
a medicinal liquid preparation intended for use in an atomizer

nebula (verb)	fleck (verb)
	make a spot or mark onto