To figures in ancient Rome, possibly lethal (5)
I believe the answer is:
toxic
'lethal' is the definition.
(I've seen this in another clue)
'to figures in ancient rome' is the wordplay.
'figures in ancient rome' becomes 'xic' (I can't explain this - if you can you should give a lot more credence to this answer).
'to'+'xic'='TOXIC'
'possibly' is the link.
Can you help me to learn more?
(Other definitions for toxic that I've seen before include "word describing bad things" , "Harmful - cox it (anag)" , "Deadly - venomous" , "Poisonous, noxious" .)