To look back at with sorrow; feel grief or sorrowful longing for on looking back.To grieve at; be mentally distressed on account of: as, to regret one's rashness; to regret a choice made.Synonyms To rue, lament. See repentance.n. Grief or trouble caused by the want or loss of something formerly possessed; a painful sense of loss; desire for what is gone; sorrowful longing.n. Pain or distress of mind, as at something done or left undone; the earnest wish that something had not been done or did not exist; bitterness of reflection.n. Dislike; aversion.n. An expression of regret: commonly in the plural.n. A written communication expressing sorrow for inability to accept an invitation.n. Synonyms Concern, Sorrow, lamentation.n. Penitence, Compunction, etc. See repentance.