Emily Dickinson Lexicon

SIGH, n.

A single deep respiration; a long breath; the inhaling of a larger quantity of air than usual, and the sudden emission of it. This is an effort of nature to dilate the lungs and give vigor to the circulation of the blood, when the action of the heart and arteries is languid from grief depression of spirits, weakness or want of exercise. Hence sighs are indications of grief or debility.