Small stone (6)
I believe the answer is:
pebble
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">small stone</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 pebble that I've seen before include "Small roundish stone" , "A small smooth stone" , "Little rock" , "Stone on beach" , "'Small, rounded stone (6)'" .)