noun / verb
mildew
MIL-doo/ˈmɪlduː/
A thin layer of fungus that grows on damp surfaces.
Powdery mildew spreads across the damp green leaf near the shaded wall.

Etymology
Old English meledeaw meant “nectar, honeydew,” rather than fungal growth. The name was presumably transferred to fungus because it too was sticky and grew on plants.
In context
The lid of the coffin had been smashed under the weight and damp soil had poured inside. It was half rotted and full of mildew
More examples
- The towels mildewed after being left in a wet pile.
- She notices a musty smell and spots of mildew.
- Good airflow helps keep stored fabrics from mildewing.
Forms
mildew · mildews · mildewed · mildewing