One in road trashing transmitter (5)
I believe the answer is:
radio
'transmitter' is the definition.
(radio transmitter is a kind of transmitter)
'one in road trashing' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' indicates putting letters inside.
'trashing' indicates an anagram (I've seen 'trash' mean this).
'road' anagrammed gives 'rado'.
'i' inserted within 'rado' is 'RADIO'.
(Other definitions for radio that I've seen before include "Communicate with" , "Transmitter" , "It was first called the wireless" , "Sound broadcasting" , "Marconi invented it" .)