Synonyms for Riddle (same or very similar meaning)
WordNet sense 1 (a difficult problem):
conundrum, enigma, brain-teaserWordNet sense 2 (separate with a riddle, as grain from chaff):
screenWordNet sense 3 (spread or diffuse through):
diffuse, imbue, penetrate, permeate, pervade, interpenetrate, diffuseFrom the ODE community, based on WordNetadd/edit