workhorse vs dray horse

workhorse and dray horse both are nouns.

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

As nouns, dray horse is a hyponym of workhorse; that is, dray horse is a word with a more specific, narrower meaning than workhorse:

Other hyponyms of workhorse include plough horse, plow horse, draft horse, draught horse, packhorse, dobbin, farm horse.

workhorse (noun)	dray horse (noun)
a horse used for plowing and hauling and other heavy labor	horse adapted for drawing heavy loads
machine that performs dependably under heavy use