Definition of "pileus" [pi•le•us]

• Botany The umbrellalike fruiting structure forming the top of a stalked fleshy fungus, such as a mushroom; the cap. (noun)
• A brimless round skullcap worn by ancient Romans. (noun)
• See caul. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "At some point, right through here, you are going to see what is called a pileus cap right there going through the top of what would be the top of a thunderstorm, if there were as a thunderstorm there."
• "Their texture is always different from that of the pileus, which is fleshy or membranous."
• "This gives a fluted appearance to the margin of the pileus, which is very thin and membranaceous."