[ 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.

Nearby words

  1. pileous,
  2. pileous gland,
  3. piles,
  4. pileum,
  5. pileup,
  6. pilewort,
  7. pilfer,
  8. pilferage,
  9. pilgarlic,
  10. pilgrim

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. 2019

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

Science 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.