Former PM's retreat briefly Chancellor's responsibility (9)
I believe the answer is:
exchequer
'chancellor's responsibility' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'former pm's retreat briefly' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'pm's retreat' becomes 'chequers' (I've seen this before).
'briefly' means to remove the last letter.
'chequers' with its final letter taken away is 'chequer'.
'ex'+'chequer'='EXCHEQUER'
Can you help me to learn more?
(Other definitions for exchequer that I've seen before include "where the money goes" , "large supply of money" , "old government office" , "royal treasury" , "Government coffers" .)