Waugh has heartless lady in flat (6)
I believe the answer is:
evelyn
'waugh' is the definition.
(novelist Evelyn Waugh)
'heartless lady in flat' is the wordplay.
'heartless' says to hollow out the word (remove centre letters).
'in' is an insertion indicator.
'flat' becomes 'even' (level).
'lady' with its centre removed is 'ly'.
'ly' put within 'even' is 'EVELYN'.
'has' is the link.
(Other definitions for evelyn that I've seen before include "'Brideshead Revisited' - novel by . . . . . . Waugh" , "Boy's or girl's name" , "Authors John ---, --- Waugh" , "John --, gardener and diarist" , "London diarist" .)