Others keep tutor in check (9)
I believe the answer is:
restraint
'check' is the definition.
(thesaurus)
'others keep tutor' is the wordplay.
'others' becomes 'rest' (I've seen this before).
'keep' means one lot of letters goes inside another.
'tutor' becomes 'train' (I've seen this before).
'rest' enclosing 'train' is 'RESTRAINT'.
'in' acts as a link.
(Other definitions for restraint that I've seen before include "Control, restriction, curtailment" , "Limiting device" , "Reserve" , "Self-control" , "It keeps someone or something under control" .)