pileus

/ˈpaɪliəs/
noun
  1. The cap or umbrella-shaped top part of a mushroom or other fungus.
    • The pileus of this fungus is smooth and slightly sticky to the touch.
    • Under the pileus, you can see the gills where spores are produced.
    • The bright red pileus of the mushroom stood out against the green moss.
  2. A type of cloud that forms as a flat, rounded cap on top of a growing cumulus cloud, often indicating severe weather.
    • The pileus cloud appeared like a white cap above the thunderhead.
    • Meteorologists watch for pileus clouds because they can signal a storm's intensity.
    • A pileus cloud formed briefly over the mountain before the rain began.
  3. A close-fitting, brimless hat worn in ancient Greece and Rome, often associated with freed slaves.
    • In ancient Rome, a freed slave would wear a pileus as a symbol of liberty.
    • The pileus was a simple woolen cap worn by common people in classical times.
    • Coins from the Roman era sometimes depict a pileus between two daggers.
Synonyms