Duck type (7)
I believe the answer is:
mallard
'duck type' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mallard that I've seen before include "The famous steam train" , "Type of duck - world speed record holding steam engine (1938)" , "Common wild duck" , "Engine holding the world speed record for a steam locomotive, set at 123mph in 1938" , "Oldest breed of duck" .)