Sunday punch vs biff

Sunday punch and biff both are nouns.

Word	Noun	Adjective	Verb	Adverb
Sunday punch	Yes	No	No	No
biff	Yes	No	Yes	No

As nouns, biff is a hypernym of Sunday punch; that is, biff is a word with a broader meaning than Sunday punch:

Sunday punch: a hard punch that renders the opponent unable to continue boxing
biff: (boxing) a blow with the fist

Other hypernyms of Sunday punch include clout, lick, poke, punch, slug.

Sunday punch (noun)	biff (noun)
a hard punch that renders the opponent unable to continue boxing	(boxing) a blow with the fist

Sunday punch (verb)	biff (verb)
	strike, usually with the fist