Stop! ( Nautical ) (5)
(Other definitions for heave to that I've seen before include "stop at sea" , "Of ship, stop without anchoring or mooring" , "come to a stop for navy" , "(Of a sailing vessel) stop moving" .)
(Other definitions for avast that I've seen before include "Stop, nautically speaking" , "Hold fast! (naut.)" , "order for tar" , "eleven [CEASE] at sea" , "Stop! (naut.)" .)