1 [countable usually plural, uncountable]
sadness that you feel about something, especially because you wish it had not happened
I decided with some regret that it was time to move on.
It is with great regret that I must decline your offer.
to somebody's regret
I lost touch with her, much to my regret.
to say that you are unable to go to a meeting, accept an invitation etc:
My father was ill and had to send his regrets.