Insufficiency (4)
'insufficiency' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lack that I've seen before include "Be without or short of" , "Deficiency or want" , "Shortage" , "Be without, need" , "Absence, deficiency" .)
'insufficiency' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for failure that I've seen before include "miss" , "[OPPOSITE OF] success" , "Collapse; disaster" , "Fiasco" , "Lack of success, or he who lacks it" .)