Definition of regret noun from the Oxford Advanced Learner's Dictionary
regret
noun
rɪˈɡret rɪˈɡret
[uncountable, countable]a feeling of sadness or disappointment that you have because of something that has happened or something that you have done or not doneIt is with great regret that I accept your resignation.She expressed her regret at the decision.a pang/twinge of regretI have no regrets about leaving Newcastle (= I do not feel sorry about it).What is your greatest regret (= the thing that you are most sorry about doing or not doing)?He gave up teaching in 2009, much to the regret of his students.