noun, plural pilei /ˈpaɪliˌaɪ, ˈpɪliˌaɪ/ [pahy-lee-ahy, pil-ee-ahy] Show IPA , for 1, 2, 4, pileus for 3.
the horizontal portion of a mushroom, bearing gills, tubes, etc., on its underside; a cap. See diag. under mushroom
2. Zoology. a.
the umbrella or bell of a jellyfish.
3. 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.
1750–60; < Neo-Latin, special use of Latin pīleus skullcap; akin to Greek pîlos felt, felt cap