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• delta
  delta

  noun

  the fourth letter of the Greek alphabet (Δ, δ).
• Delta
  Delta

  noun

  the NATO name for a class of nuclear-powered submarines armed with multiple-warhead ballistic missiles, including those designed to strike military and industrial installations: first produced for the Soviet Navy in the 1970s; in service with the Russian Navy since 1992.

delta

¹ American  

[del-tuh] / ˈdɛl tə /

noun

• deltas
  plural

1. 

   the fourth letter of the Greek alphabet (Δ, δ).

2. the consonant sound represented by this letter.

3. the fourth in a series of items.

4. anything triangular, like the Greek capital delta (Δ).

5. Mathematics. an incremental change in a variable, as Δ or δ.

6. a nearly flat plain of alluvial deposit between diverging branches of the mouth of a river, often, though not necessarily, triangular.

   the Nile delta.

7. Also Delta a word used in communications to represent the letter D.

8. Astronomy. Delta, a star that is usually the fourth brightest of a constellation.

   The fourth brightest star in the Southern Cross is Delta Crucis.

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Delta ² American  

[del-tuh] / ˈdɛl tə /

noun

Military.

1. the NATO name for a class of nuclear-powered submarines armed with multiple-warhead ballistic missiles, including those designed to strike military and industrial installations: first produced for the Soviet Navy in the 1970s; in service with the Russian Navy since 1992.

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delta ¹ British  

/ ˈdɛltə /

noun

1. the fourth letter in the Greek alphabet (Δ, δ), a consonant transliterated as d

2. an object resembling a capital delta in shape

3. (capital when part of name) the flat alluvial area at the mouth of some rivers where the mainstream splits up into several distributaries

   the Mississippi Delta

4. maths a finite increment in a variable

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Delta ² British  

/ ˈdɛltə /

noun

1. a state of Nigeria, on the Niger river delta on the Gulf of Guinea. Capital: Asaba. Pop: 4 098 391 (2006). Area: 17 698 sq km (6833 sq miles)

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Delta ³ British  

/ ˈdɛltə /

noun

1. (foll by the genitive case of a specified constellation) usually the fourth brightest star in a constellation

2. any of a group of US launch vehicles used to put unmanned satellites into orbit

3. communications a code word for the letter d

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delta Scientific  

/ dĕl′tə /

1. A usually triangular mass of sediment, especially silt and sand, deposited at the mouth of a river. Deltas form when a river flows into a body of standing water, such as a sea or lake, and deposits large quantities of sediment. They are usually crossed by numerous streams and channels and have exposed as well as submerged areas.

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Other Word Forms

Derived Forms

• deltaic
  adjective

Inflected Forms

Nouns

• deltas
  plural

Etymology

Origin of delta

First recorded in 1150–1200; Middle English delta, deltha, from Latin delta, from Greek délta; akin to Hebrew dāleth

Explanation

Named for the fourth letter of the Greek alphabet (shaped like a triangle), a delta is a triangular area where a major river divides into several smaller parts that usually flow into a larger body of water. The first so-called delta was the Nile Delta, named by the Greek historian Herodotus. What makes a delta so special? Alluvial deposits are the rich mineral soil that can be found in the delta. Despite frequent floods, farmers often settle in a delta for this reason. Here's some more fun delta trivia: the deltoid muscles in your shoulders are named after the fourth letter of the Greek alphabet too.

Example Sentences

See Examples For:

delta Delta deltas

Norris does not use a display on his dashboard showing his progress compared with his previous lap, the so-called delta, as most other drivers do.

From BBC ● Sep. 12, 2026

“It would be fine if it wasn’t in protected areas, but they want to urbanize—badly, in my opinion—the last pristine river delta in the Mediterranean,” he said.

From Slate ● Sep. 8, 2026

Gamma measures how quickly an option’s delta changes as the underlying index moves, while net dealer gamma estimates how market makers’ exposure to the contracts they have sold, or bought, may influence their hedging activity.

From MarketWatch ● Aug. 5, 2026

One example is delta waves, the slow and rolling electrical patterns commonly associated with deep sleep.

From Science Daily ● Jul. 31, 2026

The Full-Scale Tunnel, the linchpin of the lab’s World War II drag cleanup work, continued to test everything from low-speed aircraft designed with delta wings to helicopters.

From "Hidden Figures" by Margot Lee Shetterly

CEO Ed Bastian said Delta has no regrets about its decision to opt out of Starlink Wi-Fi.

From The Wall Street Journal ● Oct. 9, 2026

Fuel is taking a chunk out of Delta Air Lines’ DAL -1.00%decrease; down pointing triangle profits.

From The Wall Street Journal ● Oct. 9, 2026

Some travelers have reported offers worth thousands of dollars in recent years after carriers including United Airlines and Delta Air Lines boosted maximum payouts in the wake of the 2017 passenger-dragging incident.

From The Wall Street Journal ● Oct. 8, 2026

“While taxiing at Los Angeles International Airport, a Delta aircraft made contact with an Air Canada aircraft,” according to the Delta statement.

From Los Angeles Times ● Oct. 6, 2026

The second woman to break the sound barrier was one of Cochran's WASPs, Jean Hixson, who flew a Delta Dagger military jet in 1958, which was against regulations.

From "Women in Space" by Karen Bush Gibson

Another 400 gigatonnes are stored in ocean sediments and river deltas.

From Science Daily ● Aug. 3, 2026

The world-renowned site features iron carbonate concretions that formed some 309 million years ago, fossilizing within them ancient creatures that had once thrived in the area's lush swamps, shallow seas and river deltas.

From Barron's ● Jun. 18, 2026

In 18 of the 40 deltas, this downward movement, known as subsidence, already exceeds local sea-level rise.

From Science Daily ● Apr. 20, 2026

That means they are also imperiling some of the world’s most important food-producing lowlands in the Nile and Mekong deltas and cities from Shanghai to New York.

From Salon ● Jul. 28, 2025

In fifth-grade history we had spent a lot of time worrying about the flooded river deltas of the ancient world.

From "Jacob Have I Loved" by Katherine Paterson

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