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mushroom

/ˈmʌʃruːm/·verb

Animated scene
Fig. 1 — The ground is bare.
01Definition

As a verb, to mushroom is to grow or multiply with sudden, alarming speed — costs mushroom, a small protest mushrooms into a movement, shanty towns mushroom on a city's edge. The image is the noun's own: fungi that appear overnight, in numbers, from nowhere. That is the colour the verb keeps — not steady growth but a fast, spreading, faintly uncontrolled increase, close to proliferate and to a sudden surge. It is almost always intransitive: things mushroom; you do not mushroom something.

02In use
  • iWhat began as a minor repair mushroomed into a full renovation.
  • iiDelivery apps have mushroomed across the city, and their numbers still proliferate.
  • iiiCosts mushroomed the moment the deadline slipped.
03Collocations
  • costs mushroom
  • mushroom into
  • mushroom overnight
  • a mushrooming population
  • spring up like mushrooms

Family mushrooming (adjective) · mushroom (noun)

04Relations

=proliferate, expand, balloon, snowball, surge

≠dwindle, shrink, contract

06TOEFL & IELTS

Mushroom is a vivid, high-value verb for Writing when you want more than 'increase': it says growth was fast, sudden, and often unwelcome or uncontrolled (costs mushroomed, informal settlements mushroomed). Use it intransitively — things mushroom; you cannot mushroom something — and often with 'into' (a dispute mushroomed into a crisis). Reserve it for negative or dramatic growth; for neutral, steady increase, grow or expand fit better.

07Asked
What does mushroom mean as a verb?
To mushroom is to grow or increase very fast and suddenly — 'costs mushroomed', 'suppliers have mushroomed across the region'. It is intransitive, so things mushroom on their own. The scene above shows the picture behind it: caps erupting and multiplying across bare ground, faster than anything grows in the ordinary way.
Is 'mushroom' positive or negative?
Usually slightly negative. Mushroom carries a note of uncontrolled or unwelcome growth — costs, tensions, debts and informal settlements mushroom, rarely good things. That connotation is what separates it from the neutral 'grow' or 'increase': mushroom says the increase was not just fast but a little out of hand.
How do you pronounce mushroom?
The stress is on the first syllable: MUSH-room. The ending has two accepted forms — a full '-room' /ruːm/ or a reduced '-rum' /rʊm/ — so both 'MUSH-room' and 'MUSH-rum' are correct. The verb and the noun are pronounced the same way.
What does 'spring up like mushrooms' mean?
It means to appear suddenly and in large numbers, seemingly overnight — 'new cafés sprang up like mushrooms'. The idiom draws on the way real fungi appear from nowhere after rain, and it is the same image that gives the verb 'mushroom' its sense of fast, unplanned spread.
What usually 'mushrooms', and how is 'mushroom into' used?
The subjects are typically things that get out of hand — costs, debts, demand, tensions, or informal settlements. The verb often takes 'into' to name the result: 'a minor dispute mushroomed into a crisis', 'a leak mushroomed into a scandal'. That pattern marks a sudden jump from small and manageable to large and serious.
What is the difference between mushroom and grow?
Grow is neutral and covers any speed of increase, natural or steady. Mushroom means to grow fast and suddenly, usually unchecked and often unwelcome. A city grows over decades; slums or costs mushroom in months. Reach for mushroom only when the speed and the loss of control are the point.