Two vehicles flanking a third one? (7)
I believe the answer is:
caravan
'flanking a third one?' is the definition.
I can't tell whether this defines the answer.
'two vehicles' is the wordplay.
'two vehicles' can mean two substitutions for 'vehicle'.
'vehicle' becomes 'cara' (I can't explain this - if you can you should give a lot more credence to this answer).
'vehicle' becomes 'van' (van is a kind of vehicle).
'cara'+'van'='CARAVAN'
Can you help me to learn more?
(Other definitions for caravan that I've seen before include "Camel train" , "Group of desert voyagers" , "Group of desert travellers" , "Mobile home" , "Home on wheels" .)