A turn performed by a student is normal (7)
I believe the answer is:
natural
'is normal' is the definition.
(similar in meaning)
'a turn performed by a student' is the wordplay.
'performed' indicates anagramming the letters.
'by' says to put letters next to each other.
'student' becomes 'l' (as in L-plates for learner drivers).
'a'+'turn'='aturn'
'aturn' with letters rearranged gives 'natur'.
'natur'+'a'+'l'='NATURAL'
(Other definitions for natural that I've seen before include "Normal - innate - instinctive" , "lacking sophistication" , "chemical-free" , "Not artificial or man-made" , "Innate, inborn" .)