Emily Dickinson Lexicon

BROOK, n. [Sax. broc, or brooc. As the sense is a stream or flowing, it may be the D. broek, G. bruch, a marsh, and allied to Gr. βρεχω, or βρυω, to rain, to pour, to flow, Eolic βρυαξ, a brook. Near the site of ancient Troy is a stream called Thymbrec, Thymbrius.]

A small natural stream of water, or a current flowing from a spring or fountain less than a river. In some parts of America, run is used in a like sense; but run is also applied to larger streams than brook.