Some rare licentiousness from a bit of a saint (5)
I believe the answer is:
relic
'a bit of a saint' is the definition.
(I've seen this before)
'some rare licentiousness from' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'RELIC' is hidden in the letters of 'rare licentiousness from'.
(Other definitions for relic that I've seen before include "One may venerate this" , "Fossil" , "Old memento" , "A survival from the past" , "Part of a holy person's body or possession" .)