cast down vs dismay

cast down is not a noun while dismay is a noun.

Word	Noun	Adjective	Verb	Adverb
cast down	No	No	Yes	No
dismay	Yes	No	Yes	No

As verbs, cast down and dismay are synonyms defined as:

Other synonyms of cast down include deject, demoralise, demoralize, depress, dispirit, get down.

cast down (noun)	dismay (noun)
	fear resulting from the awareness of danger
	the feeling of despair in the face of obstacles

cast down (verb)	dismay (verb)
lower someone's spirits; make downhearted	fill with apprehension or alarm; cause to be unpleasantly surprised
	lower someone's spirits; make downhearted