Nouns

(n)sorrow, regret, rue, ruefulnesssadness associated with some wrong done or some disappointment“he drank to drown his sorrows”, “he wrote a note expressing his regret”, “to his rue, the error cost him the game”

Verbs

(v)repent, regret, ruefeel remorse for; feel sorry for; be contrite about
(v)regretfeel sad about the loss or absence of
(v)regretdecline formally or politely“I regret I can't come to the party”
(v)regretexpress with regret“I regret to say that you did not gain admission to Harvard”