Very small container attached to back of lorry (4)
I believe the answer is:
tiny
'very small' is the definition.
(I've seen this before)
'container attached to back of lorry' is the wordplay.
'container' becomes 'tin' (tin is a kind of container**).
'attached to' is a charade indicator (letters next to each other).
'back of' suggests the final letters.
The final letter of 'lorry' is 'y'.
'tin'+'y'='TINY'
(Other definitions for tiny that I've seen before include "Underdeveloped" , "- - Tim (Dickens)" , "Little" , "Minuscule" , "Really small" .)