Calculus pioneer (5)
I believe the answer is:
euler
'calculus pioneer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for euler that I've seen before include "calculating foreigner" , "Swiss mathematician; sounds like lubricator" , "See fifty three across" , "Leonhard -, C-eighteen Swiss mathematician" , "Eighteen-hole game" .)