Alternative spelling of regrettable

plural of regretting

Written on an invitation to request that the invited person reply only if they will not attend.

(transitive) to regret doing something.

(derogatory) Sexual intercourse that was consensual at the time but is later claimed to have been rape by a participant who regrets having taken part.

In a regretful manner, with regret. / (proscribed) Unfortunately, in a manner inspiring or deserving regret; used only as a sentence adverb (to introduce and modify an entire sentence).