Carriage door, say (4)
I believe the answer is:
gait
'carriage' is the definition.
(I've seen this in another clue)
'door say' is the wordplay.
'door' becomes 'gate'.
'say' shows a homophone (sound like).
'gate' is a homophone of 'GAIT'.
(Other definitions for gait that I've seen before include "Way of walking (4)" , "Method of moving" , "Bearing" , "walkway?" , "Manner of walking or running" .)