wheel horse vs draft horse

wheel horse and draft horse both are nouns.

Word	Noun	Adjective	Verb	Adverb
wheel horse	Yes	No	No	No
draft horse	Yes	No	No	No

As nouns, draft horse is a hypernym of wheel horse; that is, draft horse is a word with a broader meaning than wheel horse:

wheel horse: a draft horse harnessed behind others and nearest the wheels of a vehicle
draft horse: horse adapted for drawing heavy loads

Other hypernyms of wheel horse include draught horse, dray horse.

wheel horse (noun)	draft horse (noun)
a draft horse harnessed behind others and nearest the wheels of a vehicle	horse adapted for drawing heavy loads