Code is a bit shortened (5)
I believe the answer is:
morse
'code' is the definition.
(Morse code)
'is a bit shortened' is the wordplay.
'is a bit' becomes 'morsel' (I've seen this before).
'shortened' means to remove the last letter.
'morsel' with its final letter taken off is 'MORSE'.
(Other definitions for morse that I've seen before include "10 [SLEUTH]" , "Code; TV detective" , "Code inventor, Samuel" , "TV inspector" , "used to transmit messages" .)