Cube; rowing boat (5)
I believe the answer is:
eight
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">cube</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(8 is a cube number)</span><br/ ><br/ >'<span class="explanation-format__original">rowing boat</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for eight that I've seen before include "Oxygen's atomic number" , "team rowing" , "Figure" , "Crew of racing shell" , "power of two" .)