Go by steamship after old man (4)
I believe the answer is:
pass
'go by' is the definition.
(synonyms)
'steamship after old man' is the wordplay.
'steamship' becomes 'ss' (nautical abbreviation).
'after' says to put letters next to each other.
'old man' becomes 'pa' (both can mean someone's father).
'ss' after 'pa' is 'PASS'.
(Other definitions for pass that I've seen before include "Pronounce (judgement)" , "Exceed; mountain route" , "Hand over < identity card" , "Transfer" , "Mountain road" .)