Smallest in amount (5)
I believe the answer is:
least
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">smallest in amount</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 least that I've seen before include "Being lowest in importance - gone stale" , "Most slight" , "Lowest or smallest" , "Steal (anag)" , "Smallest part" .)