Equally skilful with either hand (12)
I believe the answer is:
ambidextrous
'equally skilful with either hand' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ambidextrous that I've seen before include "Using either hand" , "Good with either hand" , "Equally skilful with either hand" , "Both right- and left-handed" , "Equally expert with both hands" .)