Picture riddle (5)
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I believe the answer is:
rebus
'picture riddle' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rebus that I've seen before include "Puzzling symbols, etc" , "Visual wordplay - Rankin's inspector" , "Ian Rankin's Scottish detective" , "Picture-letter puzzle" , "Enigmatic representation" .)