regret noun definition in Disappointment topic from the Oxford Advanced Learner's Dictionary

regret

 noun: Disappointment topic
[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 done It is with great regret that I accept your resignation. She expressed her regret at the decision. a pang/twinge of regret I 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.