Uniform lost in citadel (9)
I believe the answer is:
identical
'uniform' is the definition.
(I've seen this before)
'lost in citadel' is the wordplay.
'lost' indicates an anagram.
'in'+'citadel'='incitadel'
'incitadel' is an anagram of 'IDENTICAL'.
(Other definitions for identical that I've seen before include "Selfsame" , "Impossible to tell apart" , "Matching" , "uniform" , "Aid client to be the very same" .)