riddle - noun

a difficult problem

a coarse sieve (as for gravel)

riddle - verb

• pierce with many holes
• set a difficult problem or riddle
• separate with a riddle, as grain from chaff
• spread or diffuse through
• speak in riddles
• explain a riddle

riddle - thesaurus

conundrum   diffuse   enigma   imbue   interpenetrate   penetrate   permeate   pervade   screen