On a vessel (6)
I believe the answer is:
aboard
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">on a vessel</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for aboard that I've seen before include "on boat, perhaps" , "on a train, perhaps" , "... [CRUISE SHIP] here, perhaps" , "on gig, perhaps?" , "On vessel or vehicle" .)