Maiden puts on best top (4)
I believe the answer is:
acme
'top' is the definition.
(synonyms)
'maiden puts on best' is the wordplay.
'maiden' becomes 'm' (cricket abbreviation).
'puts on' means one lot of letters goes inside another (some letters put on or wear other letters).
'best' becomes 'ace'.
'm' inserted within 'ace' is 'ACME'.
(Other definitions for acme that I've seen before include "Summit of achievement" , "High point of excellence" , "'Highest point, apex (4)'" , "Top or highest point" , "Point of perfection, apex" .)