welterweight vs pugilist

welterweight and pugilist both are nouns.

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

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

Other hypernyms of welterweight include boxer.

welterweight (noun)	pugilist (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.	someone who fights with his fists for sport
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)