Ancient tax (5)
I believe the answer is:
tithe
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ancient tax</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 tithe that I've seen before include "church funding" , "Levy of one tenth of something" , "One tenth - old church tax" , "Tenth part once paid as tax" , "donation to church" .)