In Rome, fair lady provides source of poison (10)
I believe the answer is:
belladonna
'poison' is the definition.
(I know that belladonna is a type of atropine)
'in rome fair lady provides source' is the wordplay.
I cannot really understand how this works, but
'lady' could be 'ladonna' and 'ladonna' is found within the answer.
The remaining letters 'bel' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?
(Other definitions for belladonna that I've seen before include "plant" , "drug supplier" , "Could it poison" , "Boy in Lebanon destroyed" , "brought a sparkle to the eye" .)