Even without Chomsky it's snug (4)
I believe the answer is:
'it's snug' is the definition.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for cosy that I've seen before include "Comfy and snug" , "Warm and comfortable" , "With a feeling of comfort and warmth" , "Warm and snug" , "Warm, secure" .)