Shortage, scarcity (4)
I believe the answer is:
lack
I believe this is a double definition.
'shortage' is the first definition.
(a lack is a shortage of something)
'scarcity' is the second definition.
(I've seen this in another clue)
(Other definitions for lack that I've seen before include "Deficiency (of something)" , "Deficiency or want" , "Be without, need" , "Dearth" , "Absence, deficiency" .)