A nonchalant "Plenty of windows" (4)

I believe the answer is:

airy

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'a nonchalant' is the definition.
(airy can mean casual or unconcerned)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for airy that I've seen before include "Light and spacious" , "Spacious - aerial" , "Flippant" , "affecting nonchalance" , "Well ventilated; insubstantial" .)

I've seen this clue in the Evening Standard.

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