Wife that is most ample (6)
I believe the answer is:
widest
'most ample' is the definition.
('wide' can be similar in meaning to 'ample')
'wife that is' is the wordplay.
'wife' becomes 'w' (abbreviation).
'that is' becomes 'id est' ('that is' in Latin).
'w'+'idest'='WIDEST'
(Other definitions for widest that I've seen before include "Most broad" , "Broadest" , "spread maximally" , "showing maximal gap between sides" , "most off target" .)