Room on board (5)
I believe the answer is:
cabin
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">room on board</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for cabin that I've seen before include "class at sea?" , "Small room or hut" , "Small wooden shelter" , "Chalet" , "Wooden dwelling" .)