mildew

UK: /ˈmɪldjuːd/

WordReference Random House Learner's Dictionary of American English © 2026

mil•dew /ˈmɪlˌdu, -ˌdyu/   n. [uncountable]

1. Plant Diseases a cottony coating on plants, fabrics, etc., caused by fungi:
   mildew on the pages of the old diary.

v. 

2. to (cause to) become affected with mildew: [no object]
   The book had mildewed over the years.
   [~ + object]
   The book had been mildewed by moisture.

WordReference Random House Unabridged Dictionary of American English © 2026

mil•dew  (mil′do̅o̅′, -dyo̅o̅′), n. 

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

v.t., v.i. 

4. to affect or become affected with mildew.

• bef. 1000; Middle English: honeydew, mildew; Old English mildēaw, equivalent. to mil- honey (cognate with Gothic milith, akin to Latin mel, Greek méli) + dēaw dew

mil′dew′y, adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

mildew / ˈmɪlˌdjuː/ noun

1. any of various diseases of plants that affect mainly the leaves and are caused by parasitic fungi
   See also powdery mildew
2. any fungus causing this kind of disease
3. another name for mould2

verb

1. to affect or become affected with mildew

Etymology: Old English mildēaw, from mil- honey (compare Latin mel, Greek mēli) + dēaw dew

ˈmilˌdewy adjective