Motorised bicycle (5)
I believe the answer is:
moped
'motorised bicycle' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for moped that I've seen before include "Power-assisted vehicle" , "Was in low spirits about the low-powered motorbike" , "dejected" , "Mooned around" , "Languidly moved" .)