(may take a clause as object or an infinitive) to feel sorry, repentant, or upset about
2.
to bemoan or grieve the death or loss of
—n
3.
a sense of repentance, guilt, or sorrow, as over some wrong done or an unfulfilled ambition
4.
a sense of loss or grief
5.
(plural) a polite expression of sadness, esp in a formal refusal of an invitation
[C14: from Old French regrete, of Scandinavian origin; compare Old Norse grāta to weep]
usage Regretful and regretfully are sometimes wrongly used where regrettable and regrettably are meant: he gave a regretful smile; he smiled regretfully; this is a regrettable (not regretful) mistake; regrettably (not regretfully), I shall be unable to attend