Large volume of transport? (7)
I believe the answer is:
omnibus
This clue is a double definition.
'large volume' is the first definition.
'transport?' is the second definition.
(omnibus is a kind of transport)
'of' is the link.
(Other definitions for omnibus that I've seen before include "Comprehensive collection of books" , "show?" , "Collection of books reprinted in one volume" , "edition of book" , "form of transport" .)