rainforest

American  

[reyn-fawr-ist, ‐-for‐] / ˈreɪnˌfɔr ɪst, ‐ˌfɒr‐ /

Or rain forest

noun

1. a tropical forest, usually of tall, densely growing, broad-leaved evergreen trees in an area of high annual rainfall.

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rainforest British  

/ ˈreɪnˌfɒrɪst /

noun

1. Also called: selva.  dense forest found in tropical areas of heavy rainfall. The trees are broad-leaved and evergreen, and the vegetation tends to grow in three layers (undergrowth, intermediate trees and shrubs, and very tall trees, which form a canopy)

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rainforest Scientific  

/ rān′fôr′ĭst /

1. A dense evergreen forest with an annual rainfall of at least 406 cm (160 inches).

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Closer Look

Most of the world's rainforests lie near the equator and have tropical climates. However, cooler rainforests exist in the Pacific Northwest region of the United States and Canada. The world's largest rainforest is located in the Amazon River basin. The Amazon rainforest has been described as the “lungs of our planet” because it continuously recycles carbon dioxide into oxygen, with a significant percentage of the world's atmospheric oxygen being produced in this region. Besides helping to regulate the world's climate, rainforests host an extraordinary diversity of life. Scientists believe that as many as half of the Earth's different species of plants and animals are found only in the rainforests, which take up a mere 7 percent of the world's landmass. By some estimates, more than half of the Earth's original rainforests have already been burned or cut down for timber or grazing land, and more than 130 plant, animal, and insect species are thought to be going extinct daily as a result of the lost habitat. Currently 25 percent of Western pharmaceuticals are derived from tropical rainforest ingredients, and 70 percent of the plants with anticancer properties are found only in this shrinking biome.

Etymology

Origin of rainforest

First recorded in 1900–05

Explanation

A rainforest is a dense, damp forest with a huge number of different kinds of plants and animals. Scientists believe there may be millions of species in rainforests that haven't been discovered yet. There are two kinds of rainforests, tropical and temperate. Temperate rainforests are much smaller, and there are fewer of them. Most rainforests in the United States (in the Pacific Northwest and Alaska) are temperate. Tropical rainforests are remarkably wet and warm, with frequent rain and thick growth of trees and plants. Hawaii has the US's only tropical rainforests.

Example Sentences

Murray said they were "as rare as the rainforest, supporting some of the UK's rarest species".

From BBC • Mar. 16, 2026

Dr. Alvin Helden discovered the new species while conducting fieldwork in the tropical rainforest of Uganda.

From Science Daily • Mar. 11, 2026

Living in the area, I drive by it a thousand times and then I remember, “Oh yeah, there’s a rainforest in here. There’s thick stands of bamboo forest that look like Vietnam.”

From Los Angeles Times • Feb. 27, 2026

Mining, plantations, and fires have caused the clearance of large tracts of lush Indonesian rainforest, removing trees that absorbed rain and helped stabilise soil.

From Barron's • Feb. 19, 2026

Peculiarly, the abandoned land was the wettest—with its rivers, lakes, and rainforest, it should have been the best place to wait out a drought.

From "1491" by Charles C. Mann