Vessel joined with a friend in amity (4)
I believe the answer is:
ship
'vessel' is the definition.
(ship is a kind of vessel)
'joined with a friend in amity' is the wordplay.
I cannot really see how this works, but
'in' could be 'hip' (both can mean fashionable) and 'hip' is found within the answer.
A single letter 's' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ship that I've seen before include "Sea-going craft" , "Large craft" , "part of navy" , "Convey (goods); a vessel" , "Ocean-going vessel" .)