gloom vs bleakness

gloom and bleakness both are nouns.

Word	Noun	Adjective	Verb	Adverb
gloom	Yes	No	No	No
bleakness	Yes	No	No	No

As nouns, bleakness is a hyponym of gloom; that is, bleakness is a word with a more specific, narrower meaning than gloom:

Other hyponyms of gloom include cloud, bareness, desolation, nakedness.

gloom (noun)	bleakness (noun)
a feeling of melancholy apprehension	a bleak and desolate atmosphere
a state of partial or total darkness
an atmosphere of depression and melancholy