Boredom seen in pupil regularly (5)
I believe the answer is:
ennui
'boredom' is the definition.
('ennui' can be a synonym of 'boredom')
'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 "French boredom and lassitude" , "Listless boredom" , "Weary feeling" , "Feeling of dissatisfaction" , "Feeling of disaffection" .)