Summit at Chequers must end, only leaders staying (4)
I believe the answer is:
acme
'summit' is the definition.
('acme' can be a synonym of 'summit')
'at chequers must end only leaders staying' is the wordplay.
'only leaders staying' indicates taking the first letters.
The first letters of 'at chequers must end' is 'ACME'.
(Other definitions for acme that I've seen before include "Top or highest point" , "Summit of achievement" , "Height of achievement" , "crown" , "Highest level or degree attainable" .)