A solitary pupil - one (4)

I believe the answer is:

lone

'a solitary' is the definition.
(thesaurus)

'pupil one' is the wordplay.
'pupil' becomes 'l' (**).
'l'+'one'='LONE'

(Other definitions for lone that I've seen before include "Single and isolated" , "He likes to operate by himself" , "Solitary, without companions" , "The ... Ranger, fictional masked cowboy" , "Companionless" .)

I've seen this clue in the Evening Standard.

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