borrowed from Malagasy, earlier "a fractional unit of the piastre equivalent to one French franc," from iray "one" + -n-, linking particle + vy "iron" + lanja "weight"
Note: For a history of colonial and pre-colonial currency in Madagascar, see Louis Molet, "Les monnaies à Madagascar," Cahiers Vilfredo Pareto, vol. 8, no. 21 (1970), pp. 203-34.