gloom vs gloominess

gloom and gloominess both are nouns.

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

As nouns, gloom and gloominess are synonyms defined as:

Other synonyms of gloom include somberness, sombreness.

As nouns, gloom and gloominess are synonyms defined as:

Other synonyms of gloom include glumness.

gloom (noun)	gloominess (noun)
a feeling of melancholy apprehension	the quality of excessive mournfulness and uncheerfulness
a state of partial or total darkness	The property of having a frowning or scowling appearance.
an atmosphere of depression and melancholy	a feeling of melancholy apprehension
	an atmosphere of depression and melancholy