Discipline is found in celibate (8)
I believe the answer is:
chastise
'discipline' is the definition.
(thesaurus)
'is found in celibate' is the wordplay.
'found in' indicates putting letters inside.
'celibate' becomes 'chaste' ('chaste' can be similar in meaning to 'celibate').
'is' inserted into 'chaste' is 'CHASTISE'.
(Other definitions for chastise that I've seen before include "Teach Sis to scold" , "Censure severely" , "Inflict physical corrective treatment" , "discipline" , "Correct!" .)