A pricking of conscience or a feeling of regret, especially one which is slight or fleeting.
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.
The amount of avoidable loss that results from choosing the wrong action.
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).