Definitions of understanding:

• noun:   the cognitive condition of someone who understands

  Example: "He has virtually no understanding of social cause and effect"

• noun:   the capacity for rational thought or inference or discrimination
• noun:   an inclination to support or be loyal to or to agree with an opinion

  Example: "I knew I could count on his understanding"

• noun:   the statement (oral or written) of an exchange of promises

  Example: "There was an understanding between management and the workers"

• adjective:   characterized by understanding based on comprehension and discernment and empathy

  Example: "An understanding friend"