What is the meaning of Regret?

To feel sorry about (a thing that has or has not happened), afterthink: to wish that a thing had not happened, that something else had happened instead.

To feel sorry about (any thing).

To miss; to feel the loss or absence of; to mourn.

Emotional pain on account of something done or experienced in the past, with a wish that it had been different; a looking back with dissatisfaction or with longing.

Dislike; aversion.

The amount of avoidable loss that results from choosing the wrong action.

One who was invited to an event who was unable to attend, but notified the organizer of this beforehand; a nonattendee.

regret

nostalgia

regret, repentance

regret

Source: wiktionary.org