Preliminary drawing (5)
'preliminary drawing' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sketch that I've seen before include "Simple drawing" , "Outline - preliminary drawing" , "Short comic scene" , "Short account" , "result of quick draw?" .)
(Other definitions for study that I've seen before include "Den; a practice drawing" , "Swot" , "Work-room" , "(Room for) academic work" , "Dusty (anag.)" .)