Knowing a king is held in great respect (5)
I believe the answer is:
aware
'knowing' is the definition.
(thesaurus)
'a king is held in great respect' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex**).
'is held in' indicates putting letters inside.
'great respect' becomes 'awe'.
'a'+'r'='ar'
'ar' put within 'awe' is 'AWARE'.
(Other definitions for aware that I've seen before include "Acquainted with or conscious of" , "Informed; conscious" , "Having knowledge or realisation" , "Alert, conscious of" , "Attentive" .)