Dictionary.com
Thesaurus.com

Saint George's mushroom

British  

noun

  1. an edible whitish basidiomycetous fungus, Tricholoma gambosum, with a floury smell

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of Saint George's mushroom

so named because it appears earlier than most fungi, around St George's day (23 April)