Small docked tail (4)
I believe the answer is:
scut
'tail' is the definition.
(I know that scut is a type of tail)
'small docked' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'docked' becomes 'cut' (I can't explain this - if you can you should believe this answer much more).
's'+'cut'='SCUT'
Can you help me to learn more?
(Other definitions for scut that I've seen before include "Small tail as of rabbit" , "Short tail, such as rabbit's" , "Cuts into a small tail" , "Deer's tail" , "Reindeer's tail" .)