Flat obtained by a woman in the Fifties (5)
I believe the answer is:
level
'flat' is the definition.
(I know that flat can be written as level)
'a woman in the fifties' is the wordplay.
'a woman' becomes 'eve' (Eve is an example).
'in the' indicates putting letters inside.
'fifties' becomes 'll' (Roman numerals).
'eve' inserted within 'll' is 'LEVEL'.
'obtained by' is the link.
(Other definitions for level that I've seen before include "Straight, even" , "Having a flat, horizontal surface" , "Neither winning, nor losing" , "Flush" , "Flatten" .)