Definition of pileus in English:

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Pronunciation: /ˈpīlēəs/ /ˈpil/

noun (plural pilei /-lēˌī/)

The cap of a mushroom or toadstool.
Example sentences
  • CO2, levels above 1,000 ppm repress expansion of the pileus and stimulate stipe growth in a wide variety of commercially-grown species, leading to spindly mushrooms in high CO2 conditions.
  • The development is initiated as a hyphal knot of 0.2 mm or less in diameter, which rapidly develops into a tiny primordium containing the rudimentary tissues of the future pileus and stipe.
  • Their compact pilei - tight-fitting in infant plants, robust and appetizingly domed in ripe ones - have a smooth (not lamellate) undersurface and a neat, strong stem.


Mid 18th century: from Latin, literally 'felt cap'.

For editors and proofreaders

Syllabification: pi·le·us

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