Sexton in constant danger, almost in the grip of the Devil (9)
I believe the answer is:
sacristan
'sexton' is the definition.
('sacristan' can be a synonym of 'sexton')
'constant danger almost in the grip of the devil' is the wordplay.
'constant' becomes 'c' (mathematical abbreviation).
'danger' becomes 'risk' ('risk' can be a synonym of 'danger').
'almost' means to remove the last letter (most of the word but not all of it).
'in the grip of' indicates putting letters inside.
'the devil' becomes 'satan' ('Satan' can be a synonym of 'devil'**).
'c'+'risk'='crisk'
'crisk' with its last letter taken off is 'cris'.
'cris' placed into 'satan' is 'SACRISTAN'.
'in' is the link.
(Other definitions for sacristan that I've seen before include "Church official" , "Church officer in charge of sacred objects" , "Sexton" , "Church worker" , "Church officer in charge of sacred vessels etc" .)