Rescue vessel (8)
I believe the answer is:
lifeboat
'rescue vessel' is the definition.
(boat which rescues people)
This is the entire clue.
(Other definitions for lifeboat that I've seen before include "It's used to rescue people at sea" , "Take to it if the ship is sinking" , "Sea rescue craft" , "needed if ship sinks" , "I bet loaf on maritime rescue vessel" .)