Be unsteady on one's feet (6)
I believe the answer is:
totter
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">be unsteady on one's feet</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 totter that I've seen before include "Waver and threaten to fall" , "Move unsteadily; be about to fall" , "I add" , "rock" , "Maybe a mathematician" .)