Strangely guarded nature seen in student (13)
I believe the answer is:
undergraduate
'student' is the definition.
(university student)
'strangely guarded nature' is the wordplay.
'strangely' indicates an anagram.
'guarded'+'nature'='guardednature'
'guardednature' with letters rearranged gives 'UNDERGRADUATE'.
'seen in' acts as a link.
(Other definitions for undergraduate that I've seen before include "One studying for a first degree" , "University student yet to take degree" .)