Reversing three foot wagon (4)
I believe the answer is:
dray
'wagon' is the definition.
(dray is a kind of wagon)
'reversing three foot' is the wordplay.
'reversing' says the letters should be written backwards.
'three foot' becomes 'yard'.
'yard' reversed gives 'DRAY'.
(Other definitions for dray that I've seen before include "Cart used for heavy loads" , "Draught horse" , "Nest in tree" , "Cart without sides, for delivering barrels" , "Cart for carrying heavy goods" .)