Rock's a saintly individual! (5)
I believe the answer is:
stone
'rock's' is the definition.
(synonyms)
'a saintly individual' is the wordplay.
'a saintly' becomes 'st' (I am not sure about this - if you are sure you should believe this answer much more).
'individual' becomes 'one' (an individual is one person).
'st'+'one'='STONE'
Can you help me to learn more?
(Other definitions for stone that I've seen before include "Endocarp" , "Seed of e.g. cherry" , "Beryl, ruby" , "Rock; gem" , "Imperial unit of weight" .)