Guardian (9)
There are a few possibilities for this:
custodian
'guardian' is the definition.
(I know that custodian is a type of guardian)
This is the entire clue.
(Other definitions for custodian that I've seen before include "One takes care of" , "Guardian" , "Protector" , "Protector/guardian (of something)" , "museum keeper" .)
'guardian' is the definition.
(I know that sentry is a type of security guard)
This is all the clue.
(Other definitions for sentry that I've seen before include "Watchperson" , "Soldier posted to keep watch" , "Mil. guard" , "Watchman" , "Person posted to keep watch for some anticipated event" .)
(Other definitions for warden that I've seen before include "Custodian" , "Guard, keeper" , "Official with supervisory duties, as in relation to a church" , "The - (Trollope)" , "Head of certain schools, colleges, etc" .)