Riddle used as means of concealment (6)
I believe the answer is:
screen
This could be a double definition.
'riddle' is the first definition.
(I know that riddle can be written as screen)
'means of concealment' is the second definition.
'screen' can be an answer for 'concealment' (synonyms). I am not certain of the 'means of' bit.
'used as' is the link.
Can you help me to learn more?
(Other definitions for screen that I've seen before include "Conceal; show (a film)" , "put on show" , "Examine carefully to select or eliminate" , "following 28 [SILVER]" , "Censer (anag.)" .)