Go by father on ship (4)
I believe the answer is:
pass
'go by' is the definition.
(synonyms)
'father on ship' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'pa'+'ss'='PASS'
(Other definitions for pass that I've seen before include "Hand over < identity card" , "Overtake; permit" , "Don't answer a question" , "Mountain defile" , "Authorise; overtake" .)