Half a tenner (5)
I believe the answer is:
fiver
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">half a tenner</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 fiver that I've seen before include "Smallest English note" , "Hazel's brother in Watership Down" , "Where to see portrait of Elizabeth Fry" , "Bank note" , "Banknote (informal)" .)