Nautical term (6)
(Other definitions for astern that I've seen before include "Ran set (anag.)" , "Behind (a boat)" , "Towards a ship's rear" , "Towards the rear of a ship" , "Behind the back of a ship" .)
(Other definitions for avast that I've seen before include "Stop at sea" , "eleven [CEASE] at sea" , "Stop, nautically speaking" , "order for tar" , "Stop on board" .)