long horse vs gymnastic horse

long horse and gymnastic horse both are nouns.

Word	Noun	Adjective	Verb	Adverb
long horse	Yes	No	No	No
gymnastic horse	Yes	No	No	No

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

long horse: a gymnastic horse without pommels and with one end elongated; used lengthwise for vaulting
gymnastic horse: a padded gymnastic apparatus on legs

Other hypernyms of long horse include horse.

long horse (noun)	gymnastic horse (noun)
a gymnastic horse without pommels and with one end elongated; used lengthwise for vaulting	a padded gymnastic apparatus on legs