Hard old lady with Italian sweetheart (7)
I believe the answer is:
granite
'hard' is the definition.
(granite can mean as hard as granite)
'old lady with italian sweetheart' is the wordplay.
'old lady' becomes 'gran' (I've seen this before).
'with' means one lot of letters go next to another.
'italian' becomes 'it' (abbreviation for Italian).
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'gran'+'it'+'e'='GRANITE'
(Other definitions for granite that I've seen before include "Very hard type of rock" , "Get rain (anag) - rock" , "determination" , "Hard stone from Tangier" , "Tearing (anag.)" .)