Father hits the road early (4)
I believe the answer is:
past
'early' is the definition.
('past' can be similar in meaning to 'early')
'father hits the road' is the wordplay.
'father' becomes 'pa' (pa is a kind of father).
'hits the road' becomes 'st' (I can't explain this - if you can you should give a lot more credence to this answer).
'pa'+'st'='PAST'
Can you help me to learn more?
(Other definitions for past that I've seen before include "Second visitor in 5 [A CHRISTMAS CAROL]" , "Finished, gone" , "The time that has elapsed" , "Beyond" , "Days gone by" .)