Book transport for a group (7)
I believe the answer is:
omnibus
'book' is the definition.
(I've seen this before)
'transport for a group' is the wordplay.
'transport' becomes 'bus' (bus is a kind of transport).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'a group' becomes 'omni' (I can't explain this - if you can you should give a lot more credence to this answer).
'bus' after 'omni' is 'OMNIBUS'.
Can you help me to learn more?
(Other definitions for omnibus that I've seen before include "Large passenger vehicle - collection of printed works in one volume" , "Large vehicle - collected edition" , "Collection of books reprinted in one volume" , "Collection of related works reprinted in one volume" , "Large volume - public transport" .)