Miner's docked dog (6)
I believe the answer is:
collie
'dog' is the definition.
(collie is a kind of dog)
'miner's docked' is the wordplay.
'miner' becomes 'collier' (collier is a kind of miner).
'docked' means to remove the last letter (to dock can mean to remove the tail of an animal).
'collier' with its final letter removed is 'COLLIE'.
(Other definitions for collie that I've seen before include "Farm dog" , "Sheep-herding dog" , "Sheepdog with long pointed muzzle" , "Silky-coated sheepdog" , "Border dog" .)