Brass tank overturned by one key Roman lady (7)
I believe the answer is:
octavia
'lady' is the definition.
'brass tank overturned by one key roman' is the wordplay.
I cannot really see how this works, but
'by' could be 'via' (I've seen this in another clue) and 'via' is found in the answer.
'one' could be 'a' and 'a' is present in the answer.
'key' could be 'c' (I've seen this in other clues) and 'c' is present in the answer.
The remaining letters 'ot' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for octavia that I've seen before include "Wife of Nero" , "Mark Antony and Nero had wives of this name" , "Antony's wife" , "Shakespeare character" , "tragedy" .)