Obsolete gold coin (6)
I believe the answer is:
guinea
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">obsolete gold coin</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 guinea that I've seen before include "Old coin, twenty-one shillings" , "Obsolete gold coin" , "Old sum of money - west African republic" , "so-called pig that's experimentally tested?" , "Former British coin worth 21 shillings" .)