[ pahy-lee-uh s, pil-ee- ]
/ ˈpaɪ li əs, ˈpɪl i- /

noun, plural pi·le·i [pahy-lee-ahy, pil-ee-ahy] /ˈpaɪ liˌaɪ, ˈpɪl iˌaɪ/ for 1, 2, 4, pi·le·us for 3.

Mycology. the horizontal portion of a mushroom, bearing gills, tubes, etc., on its underside; a cap.
  1. the umbrella or bell of a jellyfish.
  2. pileum.
Also called cap cloud, scarf cloud. Meteorology. a small, thin cloud just above or attached to a growing cumulus cloud.
a felt skullcap worn by the ancient Romans and Greeks.

Origin of pileus

1750–60; < New Latin, special use of Latin pīleus skullcap; akin to Greek pîlos felt, felt cap
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

Examples from the Web for pileus

British Dictionary definitions for pileus

/ (ˈpaɪlɪəs, ˈpɪl-) /

noun plural -lei (-lɪˌaɪ)

the upper cap-shaped part of a mushroom or similar spore-producing body

Word Origin for pileus

C18 (botanical use): New Latin, from Latin: felt cap
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for pileus

[ pīlē-əs ]

Plural pilei (lē-ī′)

The umbrellalike fruiting structure forming the top of a fleshy fungus. It is supported by the stipe. The cap of a mushroom is a pileus.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.