Dad's at the bus terminus with a free ticket (4)
I believe the answer is:
pass
'a free ticket' is the definition.
(I've seen this in another clue)
'dad's at the bus terminus' is the wordplay.
'dad's' becomes 'pa's' (pa can mean someone's father).
'at' is a charade indicator (letters next to each other).
'the bus terminus' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'pas'+'s'='PASS'
'with' is the link.
Can you help me to learn more?
(Other definitions for pass that I've seen before include "failure in quiz" , "way through mountains" , "asked for permission to enter" , "Go by; col" , "Mountain road" .)