Perhaps emperor's taking university opening (5)
I believe the answer is:
mouth
'opening' is the definition.
(I know that mouth is a type of opening)
'perhaps emperor's taking university' is the wordplay.
'perhaps emperor' becomes 'moth' (emperor moth is a type of moth).
'taking' indicates putting letters inside.
'university' becomes 'u' (abbreviation for university).
'moth' going around 'u' is 'MOUTH'.
(Other definitions for mouth that I've seen before include "Opening; say" , "Oral cavity" , "Gob" , "Sauce" , "River ending" .)