riddle vs diffuse

riddle is a noun but diffuse is not a noun.

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

As verbs, riddle and diffuse are synonyms defined as:

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

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

riddle (adjective)	diffuse (adjective)
	(of light) transmitted from a broad light source or reflected
	spread out; not concentrated in one place
	lacking conciseness

riddle (verb)	diffuse (verb)
explain a riddle	cause to become widely known
set a difficult problem or riddle	spread or diffuse through
speak in riddles	move outward
pierce with many holes
separate with a riddle, as grain from chaff
spread or diffuse through