An old word, failing to capture a disorder (9)
I believe the answer is:
anarchism
'disorder' is the definition.
(thesaurus)
'an old word failing to capture a' is the wordplay.
I cannot quite understand how this works, but
'an' could be 'i' (Roman numeral for one) and 'i' is present in the answer.
'a' could be 'an' and 'an' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for anarchism that I've seen before include "Man's chair (anag.)" , "anti-government doctrine" , "Anti-government ideology" , "lawless attitude" , "Bakunin advocated it" .)