Other forms: toadstools
A toadstool is a mushroom, especially a poisonous one. A red toadstool, toadstools in the grass, do not touch the toadstool.
There is no biological difference at all: mushroom and toadstool are the same thing, and the word only marks whether somebody thinks it is edible. That is why no rule for telling them apart works, and why identification must be species by species.
1nountoadstoolA mushroom, especially a poisonous one.
“Red toadstools with white spots grew under the birch trees.”
toadstool is a fungus.
Middle English tode-stole, toad plus stool, from the shape and from the old association of toads with poison.
Middle English
tode-stole
English, today
toadstool
From Middle English tode-stole, tadstol, taddestol, equivalent to toad + stool. Compare dialectal English frogstool (“toadstool”), stq Poagestoul (“mushroom”) literally “frog's stool”, Dutch paddenstoel.
Etymology from Wiktionary, CC BY-SA