Importance of sex in monastery (8)
I believe the answer is:
priority
'importance' is the definition.
(thesaurus)
'sex in monastery' is the wordplay.
'sex' becomes 'it' (a common euphemism).
'in' indicates putting letters inside.
'monastery' becomes 'priory' (I've seen this before).
'it' inserted within 'priory' is 'PRIORITY'.
'of' is the link.
(Other definitions for priority that I've seen before include "First concern" , "Status establishing relative importance or urgency" , "Matter of greatest importance" , "Most urgent matter" , "preferential treatment" .)