regretful Definition

regret
verb regretted, regretting

1a. To feel sorry, repentant, distressed, disappointed, etc about (something one has done or that has happened);

Thesaurus: be sorry for, have qualms about, lament, mourn, rue, grieve, bemoan, deplore, repentkick oneself (slang).
1b. To wish that things had been otherwise.
2. To remember someone or something with a sense of loss.

noun

1a. A feeling of sorrow, repentance, distress, disappointment, etc;

Thesaurus: remorse, self-reproach, grief, sorrow, bitterness, disappointment, ruefulness, lamentation, shame, compunction, contrition, penitence, repentance.
1b. A wish that things had been otherwise.
2. A sense of loss.
3. A polite expression of sorrow, disappointment, etc, used especially when declining an invitation.

Form: regrets

Derivative: regretful
adj

Full of regret
Thesaurus: sorry, apologetic, sorrowful, remorseful, rueful, sad, conscience-stricken, mournful, ashamed, repentant, penitent, contrite.

Derivative: regretfully
adverb

Derivative: regrettable

That should be regretted; unwelcome or unfortunate.
Thesaurus: unfortunate, sad, unlucky, distressing, deplorable, shameful, sorry, lamentable, disappointing, unhappy, pitiable, woeful; Antonym: fortunate, happy.

Derivative: regrettably
adverb

Etymology: 14c: from French regreter.