boxing vs spar

boxing and spar both are nouns.

Word	Noun	Adjective	Verb	Adverb
boxing	Yes	No	No	No
spar	Yes	No	Yes	No

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

boxing: fighting with the fists
spar: making the motions of attack and defense with the fists and arms; a part of training for a boxer

Other hyponyms of boxing include professional boxing, infighting, fight, rope-a-dope, sparring.

boxing (noun)	spar (noun)
fighting with the fists	making the motions of attack and defense with the fists and arms; a part of training for a boxer
the enclosure of something in a package or box	a stout rounded pole of wood or metal used to support rigging
	any of various nonmetallic minerals (calcite or feldspar) that are light in color and transparent or translucent and cleavable