canker sore vs. ulcer

noun

Pathology.
  1. an ulceration of a mucous membrane, especially of the mouth.

noun

  1. Pathology.,  a sore on the skin or a mucous membrane, accompanied by the disintegration of tissue, the formation of pus, etc.

  2. peptic ulcer.

  3. any chronically corrupting or disrupting condition, element, etc.