gloomy vs down in the mouth

gloomy and down in the mouth both are adjectives.

Word	Noun	Adjective	Verb	Adverb
gloomy	No	Yes	No	No
down in the mouth	No	Yes	No	No

As adjectives, gloomy and down in the mouth are synonyms defined as:

Other synonyms of gloomy include blue, depressed, dispirited, down, downcast, downhearted, grim, low-spirited, low.

gloomy (adjective)	down in the mouth (adjective)
depressingly dark	filled with melancholy and despondency
filled with melancholy and despondency
causing dejection