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  

/ 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  

/ 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 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

“You can still get nice leverage funding calls by selling lower delta puts,” McElligott added.

From MarketWatch • Mar. 11, 2026

"Maybe they were washed into Jezero's lake by the river that formed the delta, or maybe they were thrown into Jezero by an impact and they're just scattered there. We're not totally sure."

From Science Daily • Jan. 27, 2026

Perseverance was dispatched to the Jezero Crater because it showed qualities that may have meant it was once conducive to life, including signs it was once a delta when Mars could sustain liquid surface water.

From BBC • Nov. 28, 2025

The country is essentially a large delta crossed by three major rivers, the Rhine, Schelde, and Maas, that flow into the unpredictable North Sea.

From Barron's • Nov. 7, 2025

And Ethir Anduin he saw, the mighty delta of the River, and myriads of sea-birds whirling like a white dust in the sun, and beneath them a green and silver sea, rippling in endless lines.

From "The Fellowship of the Ring" by J.R.R. Tolkien

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