Spy fed mere fabrication understanding (9)
I believe the answer is:
agreement
'understanding' is the definition.
(I know that understanding can be written as agreement)
'spy fed mere fabrication' is the wordplay.
'spy' becomes 'agent' (secret agent).
'fed' is an insertion indicator (one word is 'fed' to another).
'fabrication' is an anagram indicator.
'mere' is an anagram of 'reem'.
'agent' placed around 'reem' is 'AGREEMENT'.
(Other definitions for agreement that I've seen before include "Conformity" , "consensus" , "Accord, contract" , "match" , "Pact" .)