1. Being, inducing, or marked by the one of the five basic taste sensations that is peculiarly acrid, astringent, and often disagreeable and characteristic of citrus peels, unsweetened cocoa, black coffee, mature leafy greens (such as kale or mustard), or ale.
  2. Distasteful or distressing to the mind.
  3. Marked by intensity or severity.
  4. Accompanied by severe pain or suffering.
  5. Being relentlessly determined.
  6. Exhibiting intense animosity.
  7. Harshly reproachful.
  8. Marked by cynicism and rancor.
  9. Intensely unpleasant especially in coldness or rawness.
  10. Caused by or expressive of severe pain, grief, or regret.

The emotion of Bitter is found in the Stomach meridian in the Earth element.

Definition from Dictionary by Merriam-Webster.