Poetic ship, British lifeboat (4)
I believe the answer is:
bark
'poetic ship' is the definition.
(archaic or poetic term for a boat)
'british lifeboat' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'lifeboat' becomes 'ark'.
'b'+'ark'='BARK'
(Other definitions for bark that I've seen before include "Shout aggressively" , "Animal sound - layer protecting tree trunk" , "Covering of tree trunk" , "Tree-skin or dog noise" , "Outside of a tree" .)