pole horse vs dray horse

pole horse and dray horse both are nouns.

Word	Noun	Adjective	Verb	Adverb
pole horse	Yes	No	No	No
dray horse	Yes	No	No	No

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

pole horse: a draft horse harnessed alongside the shaft or pole of a vehicle
dray horse: horse adapted for drawing heavy loads

Other hypernyms of pole horse include draft horse, draught horse.

pole horse (noun)	dray horse (noun)
a draft horse harnessed alongside the shaft or pole of a vehicle	horse adapted for drawing heavy loads
the horse having a starting position next to the inside rail in a harness race