axle

noun4

1. •
   The pin or spindle on which a wheel revolves, or which revolves with a wheel.

   • The mechanic replaced the broken axle on the truck.
2. •
   A transverse bar or shaft connecting the opposite wheels of a car or carriage; an axletree.
3. •
   (no longer used) An axis.
4. •
   (no longer used) Shoulder.