Meaning of wheel horse

wheel' horse"

Pronunciation: [key]
  1. Also calleda horse, or one of the horses, harnessed behind others and nearest the front wheels of a vehicle.
  2. the left-hand horse of a pair hitched to a wagon or plow.
  3. a reliable, diligent, and strong worker.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.