Mathematical symbol: short symbol written by scholar (5)
I believe the answer is:
sigma
'mathematical symbol' is the definition.
(symbol for summation in mathematics)
'short symbol written by scholar' is the wordplay.
'short' means to remove the last letter.
'symbol' becomes 'sign' (I've seen this before).
'written by' is a charade indicator (letters next to each other).
'scholar' becomes 'ma'.
'sign' with its last letter taken off is 'sig'.
'sig'+'ma'='SIGMA'
(Other definitions for sigma that I've seen before include "character in Corfu" , "Greek letter used as summation sign" , "Allowing no relaxation" , "Athenian character" , "character abroad" .)