| 1. | a stationary cloud directly above an isolated mountain peak. Compare banner cloud, crest cloud. |
| 2. | pileus (def. 3). |
[pahy-lee-uh
s, pil-ee-] 
[pahy-lee-ahy, pil-ee-ahy] for 1, 2, 4, pi⋅le⋅us for 3. | 1. | Mycology. the horizontal portion of a mushroom, bearing gills, tubes, etc., on its underside; a cap. |
| 2. | Zoology.
|
| 3. | Also called cap cloud, scarf cloud. Meteorology. a small, thin cloud just above or attached to a growing cumulus cloud. |
| 4. | a felt skullcap worn by the ancient Romans and Greeks. |
| pileus (pī'lē-əs) Pronunciation Key
Plural pilei (pī'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. |