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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. 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 ² 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 ³ British  

/ dɛlˈteɪɪk, 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

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

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

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

Fishermen working the sea between the Irrawaddy delta and the coast of Mon state found several other bodies nine days later.

From BBC ● Jul. 17, 2026

Between the islands ran branches of the Ota River as it fanned out into a delta near the sea.

From "Bomb" by Steve Sheinkin

In travel news this week, Delta announced plans to start seasonal service between Austin, Texas, and Paris in late March.

From The Wall Street Journal ● Aug. 14, 2026

A recent online search showed that a one-way Delta Airlines flight from Los Angeles International Airport to John F. Kennedy International Airport in September cost $168.

From Los Angeles Times ● Aug. 14, 2026

Delta had only a handful of price categories on the shelf.

From MarketWatch ● Aug. 13, 2026

Delta and United have been among the pioneers of segmentation in economy, and they’ve also focused on attracting richer flyers.

From MarketWatch ● Aug. 13, 2026

The blue Delta symbol glowed on the top when she booted it up.

From "The Last Olympian" by Rick Riordan

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

A new study published in Nature finds that many of the world's largest river deltas are subsiding more quickly than global sea levels are rising, putting hundreds of millions of people at potential risk.

From Science Daily ● Apr. 20, 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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