Shape of this vessel is in good order (4)
I believe the answer is:
ship
'shape of this vessel is in good order' is the definition.
'ship' can be an answer for 'vessel' (ship is a kind of vessel). I am unsure of the rest of the definition.
'shape of this vessel is in' is the wordplay.
'shape of this vessel' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'is in' becomes 'hip' (both can mean fashionable).
's'+'hip'='SHIP'
Can you help me to learn more?
(Other definitions for ship that I've seen before include "part of navy" , "eg QE2" , "See 18" , "Navigable vessel" , "craft of 1d [ADVENTURE]" .)