Definitions of limb:

• noun:   the graduated arc that is attached to an instrument for measuring angles

  Example: "The limb of the sextant"

• noun:   either of the two halves of a bow from handle to tip

  Example: "The upper limb of the bow"

• noun:   one of the jointed appendages of an animal used for locomotion or grasping: arm; leg; wing; flipper
• noun:   (astronomy) the circumferential edge of the apparent disc of the sun or the moon or a planet
• noun:   any of the main branches arising from the trunk or a bough of a tree
• noun:   any projection that is thought to resemble an arm
• name:  A surname (very rare: popularity rank in the U.S.: #26355)