Teacher in wig, retired by university (4)
I believe the answer is:
guru
'teacher' is the definition.
(I have seen 'Religious teacher' mean 'guru' so perhaps 'teacher' could also mean 'guru')
'wig retired by university' is the wordplay.
'wig' becomes 'rug' (rug is a slang term for a wig).
'retired' says the letters should be written backwards.
'by' says to put letters next to each other.
'university' becomes 'u'.
'rug' reversed gives 'gur'.
'gur'+'u'='GURU'
'in' acts as a link.
(Other definitions for guru that I've seen before include "Wise leader" , "Hindu or Buddhist spiritual teacher" , "Swami" , "Revered mentor" , "Authoritative source" .)