Security required around Saint, Russian Saint (5)
I believe the answer is:
basil
'saint' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for basil that I've seen before include "Herb - Mr Fawlty" , "Herb of mint family" , "Doctor of the fourth century" , "Mediterranean herb" , "Fellow" .)