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