Not having the necessary means or know-how (6)
I believe the answer is:
unable
'not having the necessary means or know-how' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for unable that I've seen before include "Not strong enough" , "Having insufficient strength or ability (to do something)" , "Lacking power (to do something)" , "Not fit or competent" , "Impotent" .)