Double-edged (6)
I believe the answer is:
ironic
'double-edged' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ironic that I've seen before include "Wry, sarcastic" , "Suggesting the opposite for humorous effect" , "Wryly satirical" , "Strangely apt or inapt" , "Conveying meaning by saying its opposite" .)