Walk like a duck (6)
I believe the answer is:
waddle
'walk like a duck' is the definition.
(ducks waddle when they walk)
This is all the clue.
(Other definitions for waddle that I've seen before include "Walk, taking short steps, rocking from side to side" , "Walk swayingly" , "Clumsy swaying walk" , "Walk like duck, fat man" , "Walk with clumsily swaying motion" .)