fungible

from WordNet (r) 3.0 (2006)

fungible
    adj 1: of goods or commodities; freely exchangeable for or
           replaceable by another of like nature or kind in the
           satisfaction of an obligation
    n 1: a commodity that is freely interchangeable with another in
         satisfying an obligation

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

FUNGIBLE. A term used in the civil, French, and Scotch law, it signifies 
anything whatever, which consists in quantity, and is regulated by number, 
weight, or measure; such as corn, wine, or money.. Hein. Elem. Pand. Lib. 
12, t. 1, Sec. 2;.1 Bell's Com. 225, n. 2; Ersk. Pr. Scot. Law, B. 3, t. 1, 
Sec. 7; Poth. Pret de Consomption, No. 25; Dict. de Jurisprudence, mot 
Fongible Story, Bailm, Sec. 284; 1 Bouv. Inst. n. 987, 1098.