S: (n) problem (a question raised for consideration or solution) "our homework consisted of ten problems to solve"
S: (n) question, head (the subject matter at issue) "the question of disease merits serious discussion"; "under the head of minor Roman poets"
S: (n) subject, topic, theme (the subject matter of a conversation or discussion) "he didn't want to discuss that subject"; "it was a very sensitive topic"; "his letters were always on the theme of love"
S: (v) riddle (set a difficult problem or riddle) "riddle me a riddle"
S: (v) riddle, screen (separate with a riddle, as grain from chaff)
S: (v) permeate, pervade, penetrate, interpenetrate, diffuse, imbue, riddle (spread or diffuse through) "An atmosphere of distrust has permeated this administration"; "music penetrated the entire building"; "His campaign was riddled with accusations and personal attacks"