Scholar takes this after dropping one school subject (5)
I believe the answer is:
maths
'school subject' is the definition.
(I've seen this before)
'scholar takes this after dropping one' is the wordplay.
'scholar' becomes 'ma' (**).
'takes' says to put letters next to each other.
'after dropping' is a deletion indicator.
'one' becomes 'i' (Roman numeral).
'this' with 'i' removed is 'ths'.
'ma'+'ths'='MATHS'
(Other definitions for maths that I've seen before include "It concerns numbers, in short" , "Study of numbers and sums" , "Numbers subject" , "18 across subject" , "subject, in short" .)