Banter is not good at home over time (8)
I believe the answer is:
badinage
'banter' is the definition.
(badinage is a kind of banter)
'not good at home over time' is the wordplay.
'not good' becomes 'bad' (bad is the opposite of good).
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'time' becomes 'age' (an age is a period of time).
'bad'+'in'+'age'='BADINAGE'
'is' acts as a link.
(Other definitions for badinage that I've seen before include "Beg Diana with good-humoured teasing" , "A big Dane given to banter" , "Beg Diana for light banter" , "Frivolous backchat" , "Amiable banter" .)