The word(s) "regret" appears 17 time(s) in 17 verse(s) in Quran in Mohsin Khan translation.

(11) Until, when We open for them the gate of severe punishment, then lo! they will be plunged into destruction with deep regrets, sorrows and in despair.

(12) But they killed her, and then they became regretful.

(13) And on the Day when the Hour will be established, the Mujrimun (disbelievers, sinners, criminals, polytheists) will be plunged into destruction with (deep regrets, sorrows, and) despair.

(14) Those who were deemed weak will say to those who were arrogant: "Nay, but it was your plotting by night and day: when you ordered us to disbelieve in Allah and set up rivals to Him!" And each of them (parties) will conceal their own regrets (for disobeying Allah during this worldly life), when they behold the torment. And We shall put iron collars round the necks of those who disbelieved. Are they requited aught except what they used to do?

(15) (The torment) will not be lightened for them, and they will be plunged into destruction with deep regrets, sorrows and in despair therein.

(16) O you who believe! If a Fasiq (liar - evil person) comes to you with any news, verify it, lest you should harm people in ignorance, and afterwards you become regretful for what you have done.

(17) Were it Our Will, We could crumble it to dry pieces, and you would be regretful (or left in wonderment) [Tafsir Ibn Kathir].