Ancient cipher, sort I cracked (11)
I believe the answer is:
prehistoric
'ancient' is the definition.
(I know that ancient can be written as prehistoric)
'cipher sort i cracked' is the wordplay.
'cracked' is an anagram indicator.
'cipher'+'sort'+'i'='ciphersorti'
'ciphersorti' anagrammed gives 'PREHISTORIC'.
(Other definitions for prehistoric that I've seen before include "Extremely old" , "Very old or out of date" , "very early" , "Ancient" , "antiquated" .)