Definition of "pileus"

The stem is easily separable from the pileus at its junction, in this respect being similar to Amanita, Amanitopsis, Lepiota and others.

1903, George Francis Atkinson, chapter VII, in Studies of American Fungi. Mushrooms, Edible, Poisonous, etc.‎, 2nd edition, New York: Henry Holt

One must check the size and shape of the pileus as well as its color. Many weird and unexpected shapes are found in the mushroom kingdom.

1994, Barry H. Rumack, David G. Spoerke, Handbook of Mushroom Poisoning: Diagnosis and Treatment, CRC Press, page 75

The most short-lived of all the accessory clouds, pileus is also the most beautiful.

2011, Gavin Pretor-Pinney, The Cloud Collector's Handbook, Hachette UK

Among the Romans the cap of felt was the emblem of liberty. When a slave obtained his freedom he had his head shaved, and wore instead of his hair an undyed pileus.

1859, William Smith, editor, Dictionary of Greek and Roman Antiquities, page 920