Definitions of back:

• noun:   the position of a player on a football team who is stationed behind the line of scrimmage
• noun:   a support that you can lean against while sitting

  Example: "The back of the dental chair was adjustable"

• noun:   the part of a garment that covers your back

  Example: "They pinned a `kick me' sign on his back"

• noun:   the posterior part of a human (or animal) body from the neck to the end of the spine

  Example: "His back was nicely tanned"

• noun:   the part of something that is furthest from the normal viewer

  Example: "He stood at the back of the stage"

• noun:   (football) a person who plays in the backfield
• noun:   the side that goes last or is not normally seen

  Example: "He wrote the date on the back of the photograph"

• noun:   the front and back covering of a book
• noun:   the series of vertebrae forming the axis of the skeleton and protecting the spinal cord

  Example: "The fall broke his back"

• verb:   establish as valid or genuine

  Example: "Can you back up your claims?"

• verb:   support financial backing for

  Example: "Back this enterprise"

• verb:   be behind; approve of

  Example: "I backed Kennedy in 1960"

• verb:   be in back of

  Example: "My garage backs their yard"

• verb:   shift to a counterclockwise direction

  Example: "The wind backed"

• verb:   strengthen by providing with a back or backing
• verb:   travel backward

  Example: "Back into the driveway"

• verb:   cause to travel backward

  Example: "Back the car into the parking spot"

• verb:   give support or one's approval to

  Example: "I can't back this plan"

• verb:   place a bet on

  Example: "Which horse are you backing?"

• adverb:   in or to or toward a past time

  Example: "Set the clocks back an hour"

• adverb:   at or to or toward the back or rear

  Example: "He moved back"

• adverb:   in repayment or retaliation

  Example: "We paid back everything we had borrowed"

• adverb:   in or to or toward a former location

  Example: "She went back to her parents' house"

• adverb:   in or to or toward an original condition

  Example: "He went back to sleep"

• adverb:   in answer

  Example: "He wrote back three days later"

• name:  A surname (rare: 1 in 33333 families; popularity rank in the U.S.: #3655)