1. (verb) To mourn the loss or death of. To miss very much.
  2. (verb) To be very sorry for.
  3. Sorrow aroused by circumstances beyond one’s control or power to repair
  4. An expression of distressing emotion (such as sorrow).
  5. Feel sad, repentant, or disappointed over (something that one has done or failed to do).

The emotion of Regret is found in the Lung meridian in the Metal element.

Definition from Dictionary by Merriam-Webster and Oxford Dictionary.