downcast vs depressed

downcast is a noun but depressed is not a noun.

Word	Noun	Adjective	Verb	Adverb
downcast	Yes	Yes	No	No
depressed	No	Yes	No	No

As adjectives, downcast and depressed are synonyms defined as:

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

downcast (noun)	depressed (noun)
a ventilation shaft through which air enters a mine

downcast (adjective)	depressed (adjective)
filled with melancholy and despondency	filled with melancholy and despondency
directed downward	lower than previously
	flattened downward as if pressed from above or flattened along the dorsal and ventral surfaces