Loyalty from a duke thus, protecting queen (9)
I believe the answer is:
adherence
'loyalty' is the definition.
(I've seen this before)
'a duke thus protecting queen' is the wordplay.
'duke' becomes 'd'.
'thus' becomes 'hence' (synonyms).
'protecting' indicates putting letters inside.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'hence' enclosing 'er' is 'herence'.
'a'+'d'+'herence'='ADHERENCE'
'from' acts as a link.
(Other definitions for adherence that I've seen before include "Sticking together" , "devotion" , "loyalty" .)