mildew

American  

[mil-doo, -dyoo] / ˈmɪlˌdu, -ˌdyu /

noun

1. 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.

2. any of these fungi.

3. 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)

1. to affect or become affected with mildew.

mildew British  

/ ˈmɪlˌdjuː /

noun

1. any of various diseases of plants that affect mainly the leaves and are caused by parasitic fungi See also downy mildew powdery mildew

2. any fungus causing this kind of disease

3. another name for mould 2

---

verb

1. to affect or become affected with mildew

mildew Scientific  

/ mĭl′do̅o̅′ /

1. 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.

---

Other Word Forms

• mildewy adjective
• unmildewed adjective

Etymology

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 ) + dēaw dew

Explanation

Mildew is a kind of fungus that grows in damp environments. If you find a white, musty-smelling powder on a book that's been stored in the basement, it's probably mildew. Yuck! Mildew and mold are closely related — mildew is a less harmful kind of fungus, though both can cause breathing problems. While mildew is almost always white, mold is darker and fuzzier. Since dampness causes mildew to spread, keeping things dry (possibly with the help of a dehumidifier or air conditioner) can help prevent it. The stickiness of plant mildew helps explain the word's etymology. It comes from a root meaning "honeydew."

Example Sentences

When tested on wheat, these compounds helped protect against fungal infections such as powdery mildew.

From Science Daily • Oct. 12, 2025

Before Pregerson issued his ruling, one man testified that he’d been forced to sleep under another man’s bunk in a five-person cell, where he’d eventually developed a staph infection from the mold and mildew.

From Los Angeles Times • Dec. 12, 2024

US defender Chastain vividly remembers the conditions - "the water dripping from the ceiling, the mildew - you can smell it".

From BBC • Nov. 20, 2024

I spent Tuesday scrubbing any traces of mildew off the floors and consulting with my landlords about getting a professional in here to assess the water damage inside the ceilings and walls.

From Slate • Oct. 21, 2024

Mold and mildew stains rim the edges where water must collect.

From "Counting by 7s" by Holly Goldberg Sloan

Related Words

• blight
• mold