Old lady regretted backing state (8)
I believe the answer is:
grandeur
'state' is the definition.
(I've seen this before)
'old lady regretted backing' is the wordplay.
'old lady' becomes 'gran' (short for grandmother).
'regretted' becomes 'rued' ('rue' can be a synonym of 'regret').
'backing' shows that the letters should be reversed in order.
'rued' in reverse letter order is 'deur'.
'gran'+'deur'='GRANDEUR'
(Other definitions for grandeur that I've seen before include "Splendour or magnificence" , "The splendour of France" , "Impressiveness of appearance" , "Magnificence - rare dung (anag)" , "Greatness, perhaps ironic" .)