Stop (on board) (5)
'stop' is the definition.
(I've seen this before)
'on board' is the wordplay.
I cannot really understand how this works, but
'on' could be 'to' and 'to' is found within the answer.
The remaining letters 'heave' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(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" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">stop on board</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for avast that I've seen before include "Stop, nautically speaking" , ""stop" signal" , "Stop! (naut.)" , "Stop sailing" , "shout stopping the ship" .)