gravel vs riddle

gravel and riddle both are nouns.

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

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

Other hyponyms of gravel include mix up, stump, elude, escape.

gravel (noun)	riddle (noun)
rock fragments and pebbles	a coarse sieve (as for gravel)
	a difficult problem

gravel (verb)	riddle (verb)
be a mystery or bewildering to	explain a riddle
cover with gravel	set a difficult problem or riddle
cause annoyance in; disturb, especially by minor irritations	speak in riddles
	pierce with many holes
	separate with a riddle, as grain from chaff
	spread or diffuse through