Sentence:  A scant half mile away Shelley and Mary were doubtless sitting on their diminutive terrace , the <WSD>air</WSD> about them scented with stock , and listening to the nightingale who had nested in the big lime tree at the foot of the garden . 
Meaning of the word marked with <WSD> tags:  a mixture of gases (especially oxygen) required for breathing; the stuff that the wind consists of