Not squishy (4)
I believe the answer is:
hard
'not squishy' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hard that I've seen before include "to be listened to in Scotland" , "Solid, firm, rigid" , "Firm, rigid, road leading to foreshore" , "Novel featuring Mr Gradgrind" , "Firm; demanding; stern" .)