Just retaining King's ascetic (5)
I believe the answer is:
fakir
'ascetic' is the definition.
(thesaurus)
'just retaining king's' is the wordplay.
'just' becomes 'fair' ('fair' is associated in meaning with 'just').
'retaining' indicates putting letters inside.
'king' becomes 'k'.
'fair' placed around 'k' is 'FAKIR'.
(Other definitions for fakir that I've seen before include "Holy man of the East" , "Muslim or Hindu mendicant holy man" , "Eastern holy man" , "Ascetic type" , "Muslim ascetic - Hindu holy man" .)