carthorse

noun

Etymology: From Middle English carthors, cartehors, from Old English crætehors (“a carthorse”), equivalent to cart + horse.

1. A large, strong horse used for pulling heavy loads.

   “The blacksmith's forge shone bright on the opposite side of the way, and the proprietor had the hind-leg of a carthorse in his leather-coated lap.”

   “He is not a man of independent fortune, for he works like a carthorse.”