Large former lover nervous to eat four (9)
I believe the answer is:
extensive
'large' is the definition.
('extensive' can be similar in meaning to 'large')
'former lover nervous to eat four' is the wordplay.
'former lover' becomes 'ex'.
'nervous' becomes 'tense' ('tense' can be similar in meaning to 'nervous'**).
'to eat' means one lot of letters goes inside another.
'four' becomes 'iv' ('IV' can be a synonym of 'four').
'tense' placed around 'iv' is 'tensive'.
'ex'+'tensive'='EXTENSIVE'
(Other definitions for extensive that I've seen before include "Far-reaching, wide" , "Broad in scope" , "Covering a large area" , "Widespread" , "Comprehensive" .)