Goes after a companion on the wild seas (6)
I believe the answer is:
chases
'goes after' is the definition.
('chase' can be a synonym of 'go after')
'a companion on the wild seas' is the wordplay.
'a companion' becomes 'ch' (Companion of Honour).
'on' means one lot of letters go next to another.
'the wild' indicates an anagram.
'seas' is an anagram of 'ases'.
'ch'+'ases'='CHASES'
(Other definitions for chases that I've seen before include "Follows in order to catch" , "performs follow-up" , "Pursues or follows" , "Runs after, pursues" .)