[ mil-doo, -dyoo ]
/ ˈmɪlˌdu, -ˌdyu /
Save This Word!
See synonyms for: mildew / mildewed / mildewing / mildewy on Thesaurus.com


Plant Pathology. a disease of plants, characterized by a cottony, usually whitish coating on the surface of affected parts, caused by any of various fungi.
any of these fungi.Compare downy mildew, powdery mildew.
any of similar coatings or discolorations, caused by fungi, as that which appears on fabrics, paper, leather, etc., when exposed to moisture.

verb (used with or without object)

to affect or become affected with mildew.



Apostrophes can be tricky; prove you know the difference between it’s and its in this crafty quiz!
Question 1 of 12
On the farm, the feed for chicks is significantly different from the roosters’; ______ not even comparable.

Origin of mildew

before 1000; Middle English: honeydew, mildew; Old English mildēaw, equivalent to mil- honey (cognate with Gothic milith, akin to Latin mel,Greek méli) + dēawdew
mildewy, adjectiveun·mil·dewed, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

British Dictionary definitions for mildew

/ (ˈmɪlˌdjuː) /


any of various diseases of plants that affect mainly the leaves and are caused by parasitic fungiSee also downy mildew, powdery mildew
any fungus causing this kind of disease
another name for mould 2


to affect or become affected with mildew
mildewy, adjective
Old English mildēaw, from mil- honey (compare Latin mel, Greek mēli) + dēaw dew
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for mildew

[ mĭldōō′ ]

Any of various fungi or oomycete organisms that form a white or grayish coating on surfaces, such as plant leaves, cloth, or leather, especially under damp, warm conditions. Powdery mildews are important plant diseases usually caused by ascomycete fungi, while downy mildews, including a serious disease of grapevines, are caused by oomycetes.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
What's This Word?