Definitions of itch:

• noun:   an irritating cutaneous sensation that produces a desire to scratch
• noun:   a strong restless desire
• noun:   a contagious skin infection caused by the itch mite; characterized by persistent itching and skin irritation

  Example: "He has a bad case of the itch"

• verb:   have or perceive an itch

  Example: "I'm itching--the air is so dry!"

• verb:   have a strong desire or urge to do something

  Example: "She is itching to start the project"

• verb:   scrape or rub as if to relieve itching