Guarantee wife complete autonomy in the end (8)
I believe the answer is:
warranty
'guarantee' is the definition.
(I know that guarantee can be written as warranty)
'wife complete autonomy in the end' is the wordplay.
'wife' becomes 'w' (abbreviation).
'complete' becomes 'arrant' (old-fashioned term meaning complete or utter).
'in the end' says to take the final letters.
The last letter of 'autonomy' is 'y'.
'w'+'arrant'+'y'='WARRANTY'
(Other definitions for warranty that I've seen before include "pledge" , "Free repair document" , "Bond" , "Contract" , "Guarantee given to a purchaser" .)