crossbar vs doubletree

crossbar and doubletree both are nouns.

Word	Noun	Adjective	Verb	Adverb
crossbar	Yes	No	No	No
doubletree	Yes	No	No	No

As nouns, doubletree is a hyponym of crossbar; that is, doubletree is a word with a more specific, narrower meaning than crossbar:

crossbar: a horizontal bar that goes across something
doubletree: a crossbar on a wagon or carriage to which two whiffletrees are attached in order to harness two horses abreast

Other hyponyms of crossbar include swingletree, whiffletree, whippletree.

crossbar (noun)	doubletree (noun)
long thin horizontal crosspiece between two vertical posts	a crossbar on a wagon or carriage to which two whiffletrees are attached in order to harness two horses abreast
game equipment consisting of a horizontal bar to be jumped or vaulted over
a horizontal bar that goes across something