welterweight vs prizefighter

welterweight and prizefighter both are nouns.

Word	Noun	Adjective	Verb	Adverb
welterweight	Yes	No	No	No
prizefighter	Yes	No	No	No

As nouns, prizefighter is a hypernym of welterweight; that is, prizefighter is a word with a broader meaning than welterweight:

Other hypernyms of welterweight include gladiator.

welterweight (noun)	prizefighter (noun)
A weight class division in combat sports, for fighters heavier than those in the lightweight division and lighter than those in the middleweight division.	a professional boxer
a professional boxer who weighs between 141 and 147 pounds
a wrestler who weighs 154-172 pounds
an amateur boxer who weighs no more than 148 pounds
a weight of 28 pounds; sometimes imposed as a handicap in a horse race (such as a steeplechase)