regret-n; 2 Senses

Sense Number 1: a feeling of disappointment or remorse over past circumstances

Commentary: REGRET[+state][+emotional][+disappointment][+remorse][+about_circumstances][+past]

John has no regrets about leaving academia and starting his own company.
To her regret, the opera singer had to decline the engagement because of illness.
She had few regrets selling the old house.

PropBank: regret.01
WordNet 3.0 Sense Numbers: 1

Sense Number 2: a polite declining of an invitation

Commentary: REGRET[+event][+speech_act][+declining][+polite][+of_invitation]
NOTE: usually in the plural

Mary sends her regrets that she cannot attend today's meeting.
Please give your grandmother my regrets.
So far we have forty-two acceptances and six regrets for the wedding reception.

PropBank: NM
WordNet 0.0 Sense Numbers: 1b