Bishop first to admit sex is a temptation (4)
I believe the answer is:
bait
'a temptation' is the definition.
(bait is a kind of temptation)
'bishop first to admit sex' is the wordplay.
'bishop' becomes 'B' (abbreviation for bishop in chess).
'first to' suggests taking the first letters.
'sex' becomes 'it' (a common euphemism).
The first letter of 'admit' is 'a'.
'b'+'a'+'it'='BAIT'
'is' acts as a link.
(Other definitions for bait that I've seen before include "Food used as lure" , "Food on a hook to attract fish" , "Tempt" , "Deliberately annoy or taunt" , "Boilie, for example" .)