A as in Argentina (3)
I believe the answer is:
una
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">a as in argentina</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for una that I've seen before include "Girl's name; indefinite article (f. Italian)" , "A single Spanish" , "- Stubbs, Eng. actress" , "lady" , "woman" .)