delta

¹ American  

[del-tuh] / ˈdɛl tə /

noun

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  

/ 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 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

• deltaic adjective

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

The study identifies groundwater depletion as the strongest overall factor linked to delta subsidence, although the main cause varies by region.

From Science Daily • Apr. 20, 2026

To simplify, being delta neutral means option dealers will shift their holdings of the underlying asset as option prices move in order to maintain a hedged position.

From MarketWatch • Apr. 20, 2026

The Great Valley Farm Partnership, a coalition of Central Valley farmers and water agencies, has identified 75 miles of channels, mostly in the southern delta, as priority areas for dredging.

From The Wall Street Journal • Apr. 17, 2026

She told the court how when she worked at Shell, the company was having big problems dealing with oil spills in the Niger delta area where her family was from.

From BBC • Apr. 13, 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

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