What does fungus mean?
A fungus is a spore-producing organism — such as a mushroom, mould, yeast, or mildew — that belongs to its own biological kingdom, separate from plants and animals. Lacking chlorophyll, fungi cannot make their own food; instead they absorb nutrients from organic matter, whether decaying leaves, damp walls, bread, or living tissue. This feeding habit makes them essential decomposers in nearly every ecosystem, recycling nutrients that other life depends on, while a few species act as pathogens, causing crop blights and human infections like athlete's foot. The word is singular, with 'fungi' as its usual plural, and appears both in technical biology and in everyday talk about mouldy bathrooms or lawn toadstools. Once classified as plants, fungi proved so distinctive — their cell walls contain chitin, closer to animal chemistry than plant — that scientists granted them their own kingdom, making them some of the most important, and most overlooked, organisms on Earth.
nounAny of a group of spore-producing organisms — including mushrooms, moulds, yeasts, and mildews — that feed on organic matter and lack chlorophyll, classified in their own biological kingdom (Fungi), distinct from plants and animals.
- A member of the kingdom Fungi: any spore-bearing organism such as a mushroom, mould, yeast, or mildew that absorbs nutrients from organic matter.
- (Informal/medical) A fungal growth or infection on a living host, such as athlete's foot or a fungal nail infection.
"A pale fungus spread across the damp bark of the fallen log."
"The humid basement walls were soon speckled with a black fungus."
"The doctor explained that the persistent rash was caused by a common skin fungus."
'Fungi' is the standard plural, especially in scientific and formal writing; 'funguses' also occurs but is much less common. In British English 'fungi' is typically pronounced /ˈfʌndʒaɪ/, while American usage varies between /ˈfʌŋɡaɪ/ and /ˈfʌŋɡiː/.
"Autumn rains brought a profusion of fungi to the forest floor."
Fungi are neither plant nor animal — genetically they're more closely related to you than to the moss on your garden wall.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of fungus
The English word 'fungus' comes directly from Latin 'fungus', meaning mushroom or fungus, adopted into scientific and general use in the early modern period, around the sixteenth and seventeenth centuries. Latin writers themselves used the term, though its ultimate pre-Latin origin remains uncertain. The related adjective 'fungal' and forms like 'fungoid' were later coined from the same Latin root, and the plural 'fungi' preserves the Latin inflection unchanged in scientific usage.
Related word forms
How fungus is actually used
In scientific writing 'fungus' is strictly singular, with 'fungi' as the standard plural in formal contexts ('funguses' also occurs but is less common). In everyday speech people often use 'fungus' loosely for any visible patch of mould or growth, while biologists reserve it for members of kingdom Fungi. Note that 'fungal' has largely displaced the older adjective 'fungous'.
Easily confused with fungus
'Fungi' is the plural of 'fungus' (and also the name of the biological kingdom), so it refers to multiple organisms rather than a single one.