European leader not primarily a numbers whizz (5)
I believe the answer is:
euler
'numbers whizz' is the definition.
The definition suggests a singular noun which matches the answer.
'european leader not primarily a' is the wordplay.
'european' becomes 'E' (abbreviation e.g. EU).
'leader' becomes 'ul' (I can't explain this - if you can you should give a lot more credence to this answer).
'not primarily' means to remove the first letter.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'per' with its first letter removed is 'er'.
'e'+'ul'+'er'='EULER'
Can you help me to learn more?
(Other definitions for euler that I've seen before include "Swiss mathematician; sounds like lubricator" , "Leonhard -, Eighteenth century Swiss mathematician" , "Leonhard -, C-eighteen Swiss mathematician" , "See fifty three across" , "Leonhard -----, founder of mathematical analysis" .)