Be buoyant (5)
I believe the answer is:
float
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">be buoyant</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 float that I've seen before include "Drift aimlessly" , "Bob" , "Be buoyant" , "Vehicle for delivering milk" , "Not sink" .)