Arrowroot is the fecula of Maran′ta arundina′cea or West Indian arrowroot; Sex. Syst. Monandria Monogynia; Nat. Ord. Marantaceæ; a plant, which is a native of South America and the West Indies, where it is largely cultivated in gardens and provision grounds. The tubers or roots are beaten into a pulp, stirred with cold water, removing the fibres with the hand; the milky juice is passed through a fine sieve, and the starch is allowed to subside in the strained fluid. The fecula is then washed, and dried without heat. This is the Arrowroot.
Source: wiktionary