Merriam-Webster's Collegiate® Dictionary, 11th Edition
MILDEW
I. noun
Etymology: Middle English, from Old English meledēaw honeydew; akin to Old High German militou honeydew
Date: 14th century
1. a superficial usually whitish growth produced especially on organic matter or living plants by fungi (as of the families Erysiphaceae and Peronosporaceae), a fungus producing mildew, a discoloration caused by fungi, mildewy adjective
II. verb
Date: 1606
transitive verb to affect with or as if with mildew, intransitive verb to become affected with mildew