Unmarried; — over (6)
I believe the answer is:
maiden
I believe this clue is a double definition.
'unmarried' is the first definition.
(I've seen this in another clue)
'over' is the second definition.
(maiden over is a kind of over)
(Other definitions for maiden that I've seen before include "Single" , "Six dot balls" , "See 3" , "No runs are scored from this - young girl" , "No-score over" .)