Doctor returned after old king encountered an eyelet (7)
I believe the answer is:
grommet
'an eyelet' is the definition.
(I know that eyelet can be written as grommet)
'doctor returned after old king encountered' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'returned' shows that the letters should be reversed in order.
'after' is a charade indicator (letters next to each other).
'old king' becomes 'GR' (Georgius Rex, Latin for King George).
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'mo' backwards is 'om'.
'om' after 'gr' is 'grom'.
'grom'+'met'='GROMMET'
(Other definitions for grommet that I've seen before include "Eyelet's metal ring" , "Protective eyelet" , "Eyelet lining a small hole" , "Ring for hole - tube for eardrum" , "Ring of rubber to line a hole and prevent chafing" .)