Emily Dickinson Lexicon

RUSH, n.¹ [Sax. rics or risc; probably L. ruscus. The Swedish corresponding word is såf, the Hebrew סוף, usually rendered sea-weed, and applied to the Arabic gulf. Deut. i. 1. Numb. xxi. 14. This correspondence deserves notice, as illustrating certain passages in the Scriptures.]

1. A plant of the genus Juncus, of many species. The pith of the rush is used in some places for wicks to lamps and rush-lights. Encyc. The term rush is however applied to plants of various other genera beside Juncos, and by no means to all of the genus Juncus.
2. Any thing proverbially worthless or of trivial value. John Bull's friendship is not worth a rush. Arbuthnot.