Studies Italian with variable concentration (7)
I believe the answer is:
density
'concentration' is the definition.
('density' can be a synonym of 'concentration')
'studies italian with variable' is the wordplay.
'studies' becomes 'dens' (I've seen this before).
'italian' becomes 'it'.
'with' means one lot of letters go next to another.
'variable' becomes 'y' (I've seen this in other clues).
'dens'+'it'+'y'='DENSITY'
(Other definitions for density that I've seen before include "Degree of compactness" , "The compactness of a substance" , "Concentrated condition as of fog" , "Number of items in a given area" , "Concentration, compactness" .)