Citadel in ruin is the very same (9)
I believe the answer is:
identical
'is the very same' is the definition.
(I've seen this before)
'citadel in ruin' is the wordplay.
'ruin' indicates an anagram.
'citadel'+'in'='citadelin'
'citadelin' anagrammed gives 'IDENTICAL'.
(Other definitions for identical that I've seen before include "Indistinguishable" , "uniform" , "Matching" , "Selfsame" , "lacking distinction" .)