Sentence:  "If I," said Mr. Collins, "were so fortunate as to be able to sing, I should have great pleasure, I am sure, in obliging the company with an <WSD>air</WSD>; for I consider music as a very innocent diversion, and perfectly compatible with the profession of a clergyman..." 
Meaning of the word marked with <WSD> tags:  A song, especially a solo; an aria.