pileus: Meaning and Definition of

pi•le•us

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