Square Italian dish containing anchovies, primarily (6)
I believe the answer is:
piazza
'square' is the definition.
('piazza' can be a synonym of 'square')
'italian dish containing anchovies primarily' is the wordplay.
'italian dish' becomes 'pizza' (I've seen this before).
'containing' indicates putting letters inside.
'primarily' suggests taking the first letters.
The initial letter of 'anchovies' is 'a'.
'pizza' placed around 'a' is 'PIAZZA'.
(Other definitions for piazza that I've seen before include "Where Italians may gather" , "3 down" , "Public square in Italian town" .)