Want some special acknowledgement (4)
'want' is the definition.
('lack' can be a synonym of 'want')
'some special acknowledgement' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'LACK' is hidden in the letters of 'special acknowledgement'.
(Other definitions for lack that I've seen before include "Deficiency or want", "Be without, need", "Deficiency (of something)", "Be without or short of", "Dearth".)