Compartment is somewhat private and warm (4)

I believe the answer is:

snug

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'warm' is the definition.
(thesaurus)

I don't understand how the rest of the clue works.

(Other definitions for snug that I've seen before include "Well protected or concealed" , "Small bar in pub - warm and comfortable" , "Warm and cosy" , "Cosy and comfortable" , "Compact" .)

I've seen this clue in The Irish Times.

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