Gruff dog starting to turn (4)
I believe the answer is:
curt
'gruff' is the definition.
(both can mean brusque or rude)
'dog starting to turn' is the wordplay.
'dog' becomes 'cur' (a cur is an aggressive or scruffy dog).
'starting to' indicates taking the first letters.
The first letter of 'turn' is 't'.
'cur'+'t'='CURT'
(Other definitions for curt that I've seen before include "Rudely blunt" , "Brief and terse" , "Concise" , "Discourteously brief" , "Brusque, short" .)