Old public service vehicles in books (9)
I believe the answer is:
omnibuses
'books' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Maybe there's an association between them I don't understand?
'old public service vehicles' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'public service' becomes 'mni' (I can't explain this - if you can you should believe this answer much more).
'vehicles' becomes 'buses' (bus is a kind of vehicle).
'o'+'mni'+'buses'='OMNIBUSES'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for omnibuses that I've seen before include "Large volumes" , "traffic on the roads" , "public transport" .)