Yes, it can be. Dismay is a verb (to discourage or distress) or a noun (an upset, discouraged feeling). But the past participle of the verb can be used as an adjective (e.g. dismayed onlookers).
YES. Their reaction dismayed him. It can also be an adjective: He was dismayed at the change in his old friend.
There is no plural form for the noun dismay. Dismay is a state of being, you are either in that state or you are not. When you need to say that a number of people are in the state of dismay, you use the adjective form, the dismayed people, or the verb form, they were dismayed.
Downcast and dismayed, Danny felt quite dejected when dumped by his girlfriend.
He was dismayed at the thought of not seeing them again.
was dismayed to find that his partners political credit not good
No, it isn't.
Gladdened.
pleasant surprise
They were not, however, dismayed by the news. The above sentence required two commas.
Some words that rhyme with dismayed are disobeyed, blade, and grenade.
The prefix for "dismayed" is "dis-." This prefix is used to indicate a negation or reversal of the state described by the root word. In this case, "dismayed" conveys a sense of being troubled or distressed, with "dis-" suggesting a departure from a state of ease or contentment.
The antonym for "dismayed" is "reassured" or "comforted." While "dismayed" conveys feelings of shock, disappointment, or concern, its antonyms reflect a sense of calm, confidence, or relief. Other possible antonyms include "encouraged" or "elated," depending on the context.