Slim judge scratching bottom (4)
I believe the answer is:
thin
'slim' is the definition.
(I know that slim can be written as thin)
'judge scratching bottom' is the wordplay.
'judge' becomes 'think' (thinking is a kind of judging).
'scratching bottom' means to remove the last letter.
'think' with its final letter taken away is 'THIN'.
(Other definitions for thin that I've seen before include "Meagre" , "Having little width" , "Superficial" , "Unconvincing" , "Slender, slight" .)