atmosphere vs gloom

atmosphere and gloom both are nouns.

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

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

atmosphere (noun)	gloom (noun)
a distinctive but intangible quality surrounding a person or thing	a feeling of melancholy apprehension
the mass of air surrounding the Earth	a state of partial or total darkness
the envelope of gases surrounding any celestial body	an atmosphere of depression and melancholy
a unit of pressure: the pressure that will support a column of mercury 760 mm high at sea level and 0 degrees centigrade
the weather or climate at some place
a particular environment or surrounding influence