mould [2] , (U.S.) mold
n
1 a coating or discoloration caused by various saprotrophic fungi that develop in a damp atmosphere on the surface of stored food, fabrics, wallpaper, etc.
2 any of the fungi that causes this growth
vb
3 to become or cause to become covered with this growth, (Also called)
mildew
(C15: dialect (Northern English) mowlde mouldy, from the past participle of moulen to become mouldy, probably of Scandinavian origin; compare Old Norse mugla mould)