Give post to witty person travelling by estate car (7,5)
I believe the answer is:
station wagon
'estate car' is the definition.
(I've seen this before)
'give post to witty person travelling' is the wordplay.
'give' says to put letters next to each other.
'post' becomes 'station' (a station is a post).
'to witty person travelling' becomes 'wagon' (I can't justify this - if you can you should give a lot more credence to this answer).
'station' next to 'wagon' is 'STATION WAGON'.
'by' acts as a link.
Can you help me to learn more?
(Other definitions for station wagon that I've seen before include "US estate car" , "American estate car" , "American vehicle" .)