Light motorbike moved aimlessly (5)
I believe the answer is:
moped
This clue is a double definition.
'light motorbike' is the first definition.
(I've seen this before)
'moved aimlessly' is the second definition.
(I've seen this before)
(Other definitions for moped that I've seen before include "Was in low spirits about the low-powered motorbike" , "Two-wheeled vehicle" , "Mooned around" , "Two-wheeled transport -- was in low spirits" , "Light motor cycle" .)