Weariness seen in pupil regularly (5)
I believe the answer is:
ennui
'weariness' is the definition.
(thesaurus)
'seen in pupil regularly' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'seen'+'in'+'pupil'='seeninpupil'
The alternating letters of 'seeninpupil' are 'ENNUI'.
(Other definitions for ennui that I've seen before include "Feeling of listlessness" , "Boredom or discontent" , "doldrums" , "Listless feeling" , "Boredom, dullness" .)