interpenetrate vs riddle

interpenetrate is not a noun while riddle is a noun.

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

As verbs, interpenetrate and riddle are synonyms defined as:

Other synonyms of interpenetrate include diffuse, imbue, penetrate, permeate, pervade.

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

interpenetrate (verb)	riddle (verb)
penetrate mutually or be interlocked	explain a riddle
spread or diffuse through	set a difficult problem or riddle
	speak in riddles
	pierce with many holes
	separate with a riddle, as grain from chaff
	spread or diffuse through