Vehicle, not quite reaching moon (4)
I believe the answer is:
mope
'moon' is the definition.
(I've seen this before)
'vehicle not quite' is the wordplay.
'vehicle' becomes 'moped' (moped is a kind of vehicle).
'not quite' means to remove the last letter (most but not all of the word).
'moped' with its last letter taken away is 'MOPE'.
'reaching' is the link.
(Other definitions for mope that I've seen before include "Pine - sulk" , "listless person" , "Feel dejected and apathetic" , "Be listless and apathetic" , "Misery guts" .)