Crossword Genius

Lassitude seen in pupil regularly (5)

Ross

I believe the answer is:

ennui

'lassitude' is the definition.
(both can mean a feeling of weariness)

'seen in pupil regularly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'seen'+'in'+'pupil'='seeninpupil'
The alternate letters of 'seeninpupil' are 'ENNUI'.

(Other definitions for ennui that I've seen before include "tiredness" , "Result of boredom" , "to make one list less when connected" , "Feeling of weariness or boredom" , "Boredom or discontent" .)

I've seen this clue in The Telegraph.
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