Barren queen in fence crossing (7)
I believe the answer is:
sterile
'barren' is the definition.
(I've seen this before)
'queen in fence crossing' is the wordplay.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'in' indicates putting letters inside.
'fence crossing' becomes 'stile' (I've seen this before).
'er' inserted within 'stile' is 'STERILE'.
(Other definitions for sterile that I've seen before include "Unable to produce young" , "Free from living micro-organisms, absolutely clean" , "Like theatre" , "like a mule" , "Non-productive" .)