wheel horse vs draught horse

wheel horse and draught horse both are nouns.

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

As nouns, draught horse is a hypernym of wheel horse; that is, draught 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
draught horse: horse adapted for drawing heavy loads

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

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