mushrooming

UK: /ˈmʌʃruːmɪŋ/

WordReference Random House Learner's Dictionary of American English © 2025

mush•room /ˈmʌʃrum, -rʊm/   n. 

[countable]
1. Fungi a fungus that includes the toadstools and puffballs.
2. anything of similar shape or rapid growth, as a mushroom-shaped cloud of smoke from a nuclear explosion.

adj. [before a noun]

3. of or containing mushrooms.
4. resembling a mushroom in shape or rapid growth.

v. [no object]

5. to spread, grow, or develop quickly:
   Sales began to mushroom.
6. to gather mushrooms:
   to go mushrooming in the woods.

WordReference Random House Unabridged Dictionary of American English © 2025

mush•room  (mush′ro̅o̅m, -rŏŏm), n. 

1. Fungi any of various fleshy fungi including the toadstools, puffballs, coral fungi, morels, etc.
2. Fungi any of several edible species, esp. of the family Agaricaceae, as Agaricus campestris (meadow mushroom or field mushroom,) cultivated for food in the U.S.
3. anything of similar shape or correspondingly rapid growth.
4. a large, mushroom-shaped cloud of smoke or rubble, formed in the atmosphere as a result of an explosion, esp. a nuclear explosion.

adj. 

5. of, consisting of, or containing mushrooms:
   a mushroom omelet.
6. resembling a mushroom in shape or form.
7. of rapid growth and often brief duration:
   mushroom towns of the gold-rush days.

v.i. 

8. to spread, grow, or develop quickly.
9. to gather mushrooms.
10. to have or assume the shape of a mushroom.

• Middle French mousseron Late Latin mussiriōn-, stem of mussiriō
• alteration (by folk etymology, etymological) of Middle English muscheron, musseroun 1350–1400

mush′room•like′, adj. 
mush′room•y, adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

mushroom / ˈmʌʃruːm -rʊm/ noun

1. the fleshy spore-producing body of any of various basidiomycetous fungi, typically consisting of a cap (pileus) at the end of a stem arising from an underground mycelium. Some species, such as the field mushroom, are edible
   Compare pileus, toadstool
2. (as modifier): mushroom soup
3. something resembling a mushroom in shape or rapid growth
4. (as modifier): mushroom expansion

verb (intransitive)

1. to grow rapidly: demand mushroomed overnight
2. to assume a mushroom-like shape

Etymology: 15th Century: from Old French mousseron, from Late Latin mussiriō, of obscure origin