Sham public transport to go back in (5)
I believe the answer is:
bogus
'sham' is the definition.
(I've seen this before)
'public transport to go back in' is the wordplay.
'public transport' becomes 'bus' (bus is a kind of public transport).
'to go back' becomes 'og' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'bus' enclosing 'og' is 'BOGUS'.
Can you help me to learn more?
(Other definitions for bogus that I've seen before include "Phoney, not genuine" , "false impression" , "taking one for a ride?" , "Scribbled drawing" , "Sham, phoney" .)