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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. (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 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. 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 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

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Etymology

Origin of delta

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

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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

“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

Geological reconstructions indicate that the sediments containing the fossils formed in near-shore, shallow-water delta coastal environments.

From Science Daily ● Aug. 27, 2026

It’s also referred to as the delta sleep-inducing peptide.

From MarketWatch ● Jul. 24, 2026

For decades, so much water has been taken that the river seldom meets the sea in Mexico, and its delta, once filled with lush wetlands and forests, has shriveled to stretches of dry riverbed.

From Los Angeles Times ● Jul. 21, 2026

To their right, the Phlegethon split into branches that etched the plain, widening into a delta of smoke and fire.

From "The House of Hades" by Rick Riordan

American, Delta and United already do that, of course.

From The Wall Street Journal ● Oct. 16, 2026

A spokesperson for Delta said the airline "has zero tolerance for unruly or unlawful behavior, as the safety of our customers and crew always comes first."

From Barron's ● Oct. 12, 2026

A spokesperson for Delta told The Times in an emailed statement, “Delta has zero tolerance for unruly or unlawful behavior, as the safety of our customers and crew always comes first.”

From Los Angeles Times ● Oct. 12, 2026

Delta said in a statement to Variety that it has “zero tolerance for unruly or unlawful behavior,” adding that passenger and crew safety is its priority.

From Salon ● Oct. 12, 2026

It was interesting flying, and I got a chance to fly such airplanes as the North American F-100 Super Sabre, the Convair F-1Q2 Delta Dagger, the Lockheed F-104 Starfighter, and quite a few others.

From "Flying to the Moon: An Astronaut's Story" by Michael Collins

Among the most important contributors are heavy groundwater pumping, oil and gas extraction, the compression of relatively young sediments in river deltas, and the weight of expanding urban areas.

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

"Centimeters of sea level rise will greatly increase the risk of flooding in deltas," Lin said.

From Science Daily ● Oct. 23, 2025

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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