apprehension vs gloom

apprehension and gloom both are nouns.

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

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

apprehension (noun)	gloom (noun)
the act of apprehending (especially apprehending a criminal)	a feeling of melancholy apprehension
the cognitive condition of someone who understands	a state of partial or total darkness
painful expectation	an atmosphere of depression and melancholy
fearful expectation or anticipation