What's the meaning of "*billowy* blue shirt"?
This is from the book, "Call me by your name".

I shut my eyes, say the word, and I'm back in Italy, so many years ago, walking down the tree-lined driveway, watching him step out of the cab, **billowy** blue shirt, wide-open collar, sun-glasses, skin everywhere.

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I've looked up the dictionary and "billowy" means I guess either 1.characterized by great swelling waves or surges or 2. appearing large and soft or filled with air.

Is it definition 2? But I still can't quite picture it and don't really understand especially because the meaning is abstract.

Could anyone describe the image of "billowy blue shirt" in as much detail as you can so that I get a sense of what the word delivers here?

Question

What's the meaning of "*billowy* blue shirt"?
This is from the book, "Call me by your name".

I shut my eyes, say the word, and I'm back in Italy, so many years ago, walking down the tree-lined driveway, watching him step out of the cab, **billowy** blue shirt, wide-open collar, sun-glasses, skin everywhere.

-
I've looked up the dictionary and "billowy" means I guess either 1.characterized by great swelling waves or surges or 2. appearing large and soft or filled with air.

Is it definition 2? But I still can't quite picture it and don't really understand especially because the meaning is abstract.

Could anyone describe the image of "billowy blue shirt" in as much detail as you can so that I get a sense of what the word delivers here?

Answer

The person is stepping out of the taxi, and his shirt is a billowy, blue shirt. 
His shirt is blue, but it is billowing in the wind. 
This means that the wind is going in (under) his shirt and making a billowing shape, like waves, like the wind is pushing from the inside, and pushing (expanding) one section, and then that section collapses. 
The shirt is billowing - like waves that rise and fall, parts of his shirt rise and fall because the wind it lifting it up and then the wind moves and the shirt falls down. Much like a long dress might billow on a woman.