fly agaric

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A poisonous mushroom (Amanita muscaria) usually having a red or orange cap with white wartlike patches, and containing compounds that have hallucinogenic properties.

from The Century Dictionary.

• noun A species of mushroom, Agaricus muscarius, found in woods, and having a bright-red pileus studded with pale warts, while the stipe and gills are ivory-white.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A poisonous mushroom, Amanita muscaria, with a large crimson cap, fading to yellow, scattered with white flecks.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun poisonous (but rarely fatal) woodland fungus having a scarlet cap with white warts and white gills