Push part of bike, we hear (6)
I believe the answer is:
peddle
'push' is the definition.
(thesaurus)
'part of bike we hear' is the wordplay.
'part of bike' becomes 'pedal' ('pedal' is part of 'bike').
'we hear' shows a homophone (sound like).
'pedal' is a homophone of 'PEDDLE'.
(Other definitions for peddle that I've seen before include "Sell from door to door" , "Tout" , "Travelling salesman does!" , "sell my wares" , "Deal illegally in (not a lever on a cycle!)" .)