pierce vs riddle

pierce is not a noun while riddle is a noun.

Word	Noun	Adjective	Verb	Adverb
pierce	No	No	Yes	No
riddle	Yes	No	Yes	No

As verbs, riddle is a hyponym of pierce; that is, riddle is a word with a more specific, narrower meaning than pierce:

Other hyponyms of pierce include poke, puncture, prick, prickle, bite, perforate, punch, bite, prick, sting, tap.

pierce (noun)	riddle (noun)
	a coarse sieve (as for gravel)
	a difficult problem

pierce (verb)	riddle (verb)
make a hole into	explain a riddle
penetrate or cut through with a sharp instrument	set a difficult problem or riddle
cut or make a way through	speak in riddles
move or affect (a person's emotions or bodily feelings) deeply or sharply	pierce with many holes
sound sharply or shrilly	separate with a riddle, as grain from chaff
	spread or diffuse through