Tiny arachnid (4)
I believe the answer is:
mite
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">tiny arachnid</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 mite that I've seen before include "Old piece" , "Tiny arachnid, person or amount of money" , "The widow's contribution, just in time" , "Microscopic creature" , "Minute arachnid" .)