down in the mouth vs low-spirited

down in the mouth and low-spirited both are adjectives.

Word	Noun	Adjective	Verb	Adverb
down in the mouth	No	Yes	No	No
low-spirited	No	Yes	No	No

As adjectives, down in the mouth and low-spirited are synonyms defined as:

down in the mouth and low-spirited: filled with melancholy and despondency

Other synonyms of down in the mouth include blue, depressed, dispirited, down, downcast, downhearted, gloomy, grim, low.

down in the mouth (adjective)	low-spirited (adjective)
filled with melancholy and despondency	filled with melancholy and despondency