Canniness (6)
I believe the answer is:
acumen
'canniness' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for acumen that I've seen before include "Business sense" , "Being sharp" , "Ability to judge and decide quickly" , "Shrewdness, good for business" , "ability to make good judgements" .)