Leave port (3,4)
'leave port' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sail that I've seen before include "Travel by ship" , "Go by boat" , "Begin a voyage" , "Navigate" , "Fabric on a mast" .)
This clue is a double definition.
'leave' is the first definition.
(I've seen this before)
'port' is the second definition.
(I've seen this before)
(Other definitions for split that I've seen before include "Divide (into parts)" , "Cleavage" , "Divide into portions" , "share out" , "Croatian resort; rend" .)
'leave port' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for set sail that I've seen before include "Left port" , "have started journey" , "Begin a voyage" , "left land behind" , "Leave for (sea) voyage" .)