Swiss mathematician (5)
I believe the answer is:
euler
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">swiss mathematician</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for euler that I've seen before include "Leonhard --, C18 Swiss mathematician" , "Leonhard -, C-eighteen Swiss mathematician" , "Leonhard -----, founder of mathematical analysis" , "calculating foreigner" , "Swiss scientist" .)