Measure vehicle, the man needing length (6)
I believe the answer is:
bushel
'measure' is the definition.
(bushel is a kind of measure)
'vehicle the man needing length' is the wordplay.
'vehicle' becomes 'bus' (I've seen this before).
'the man' becomes 'he'.
'needing' means one lot of letters go next to another.
'length' becomes 'l'.
'bus'+'he'+'l'='BUSHEL'
(Other definitions for bushel that I've seen before include "'Don't hide your light behind a . . . . . .'" , "Old unit of dry measure (under which one hides one's light?)" , "A few pecks wanted" , "Old measure of capacity" , "Eight-gallon measure of capacity - under which one's light should not be hidden" .)