Wig returned to university teacher (4)
I believe the answer is:
guru
'teacher' is the definition.
(teacher or guide)
'wig returned to university' is the wordplay.
'wig' becomes 'rug' (rug is a slang term for a wig).
'returned' says the letters should be written in reverse.
'to university' becomes 'U' (abbreviation as in UMass).
'rug' reversed gives 'gur'.
'gur'+'u'='GURU'
(Other definitions for guru that I've seen before include "Religious leader and spiritual teacher" , "Revered mentor" , "Hindu or Buddhist spiritual teacher" , "Master, mentor" , "Spiritual guide" .)