regret [n.][v.] 後悔/遺憾

regret as a verb:  (regret that / regret to V / regret Ving)

• I regret that you see it like that. 你這樣看待這件事，我很遺憾
• I always regret staying up late because it affects my productivity the next day.
• We regret to inform you that your job application has not been successful.
• Is there anything you've done in your life that you regret? 
• 你一生中有沒有做過什麼令你感到懊悔的事情？

regret as a noun:

• She had no regrets for her actions.
• I have no regrets.

(*) I am sorry for your loss.