Clear thought shows cunning (3)
I believe the answer is:
art
'cunning' is the definition.
(I've seen this in another clue)
'clear thought shows' is the wordplay.
'shows' indicates the answer is hidden within the clue.
'ART' is hidden in the letters of 'clear thought'.
(Other definitions for art that I've seen before include "Work such as paintings or sculptures" , "For example, Blakey's creative" , "Music, painting etc" , "The works of Alma-Tadema" , "crafty conduct" .)