delta

1 of 4

noun

del·​ta ˈdel-tə 

plural deltas

1

: the 4th letter of the Greek alphabet see Alphabet Table

2

: something shaped like a capital Greek delta

especially, geology : the alluvial deposit at the mouth of a river

the Mississippi Delta

3

mathematics : an increment of a variable

—symbol Δ

4

: delta wave

During deep sleep, the brain operates in delta wave frequency. But it's difficult to go from beta to theta then delta without first switching down to a relaxed alpha state.

—Daily Mail (London)

5

or less commonly Delta : delta variant

As SARS-CoV-2 continues to spread among humans, natural selection and adaptation will result in more variants that could plausibly be more transmissible than delta.

—Suresh V. Kuchipudi

deltaic

del-ˈtā-ik 

adjective

delta

2 of 4

adjective (1)

chemistry

: fourth in position in the structure of an organic (see organic entry 1 sense 1b(2)) molecule from a particular group or atom

—symbol δ

Delta

3 of 4

communications code word

—used as a code word for the letter d

Delta

4 of 4

adjective (2)

: of, relating to, or characteristic of the The Delta region of Mississippi

Example Sentences

Recent Examples on the Web

Noun

The specimens in question come from the Mazon Creek fossil deposits of Northern Illinois, an ancient delta that preserved millions of soft-bodied organisms when they were buried rapidly in muddy sediments. —Tim Newcomb, Popular Mechanics, 8 Mar. 2023

Newsom, for example, is trying to waive environmental rules aimed at keeping juvenile salmon alive in the delta. —Los Angeles Times, 20 Feb. 2023

The depot is near the base of an ancient river delta that once flowed into Jezero Lake. —Sarah Kuta, Smithsonian Magazine, 1 Feb. 2023

And the landing was a success, placing the rover at the edge of a structure that appeared to be a river delta where the nearby highlands drained into the crater. —John Timmer, Ars Technica, 23 Nov. 2022

The city of Antioch has shown as much initiative as any Bay Area supplier, recently breaking ground on a small desalination plant in the delta with the hope of procuring 30% of its water there. —Kurtis Alexander, San Francisco Chronicle, 18 Sep. 2022

Two communities with a combined population of about 700 were threatened but no mandatory evacuations were ordered in what became the largest wildfire ever in the delta at 259 square miles (671 square kilometers). —Mark Thiessen, Anchorage Daily News, 25 July 2022

Two communities with a combined population of about 700 were threatened but no mandatory evacuations were ordered in what became the largest wildfire ever in the delta at 259 square miles. —Mark Thiessen, BostonGlobe.com, 25 July 2022

Previous strains like alpha, beta and delta fell under the convention. —Bloomberg News, oregonlive, 7 Jan. 2023

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Word History

Etymology

Noun and Adjective (1)

Middle English deltha, from Greek delta, of Semitic origin; akin to Hebrew dāleth daleth

First Known Use

Noun

12th century, in the meaning defined at sense 1

Adjective (1)

circa 1929, in the meaning defined above

Communications Code Word

1952, in the meaning defined above

Adjective (2)

1859, in the meaning defined above

Phrases Containing delta

• delta ray
• delta variant
• Kronecker delta
• delta agent
• delta virus
• delta wing
• delta wave
• delta hepatitis
• hepatitis delta virus

• delta ray
• delta variant
• Kronecker delta
• delta agent
• delta virus
• delta wing
• delta wave
• delta hepatitis
• hepatitis delta virus

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Kids Definition

delta

noun

del·​ta

ˈdel-tə

1

: the 4th letter of the Greek alphabet

—Δ or ƍ

2

: something shaped like a capital Δ

especially : the triangular or fan-shaped piece of land made by deposits of mud and sand at the mouth of a river

deltaic

del-ˈtā-ik

adjective

Medical Definition

delta

1 of 2 noun

del·​ta ˈdel-tə 

1

: the fourth letter of the Greek alphabet

—symbol Δ or ƍ

2

: any of various things felt to resemble a capital Δ

especially : the triangular terminus of a pattern in a fingerprint formed either by bifurcation of a ridge or by divergence of two ridges that are parallel beyond it

3

: delta wave

4

also Delta : delta variant

delta

2 of 2 adjective

variants or ƍ-

1

: of or relating to one of four or more closely related chemical substances

the delta chain of fetal hemoglobin

ƍ-yohimbine

—used somewhat arbitrarily to specify ordinal relationship or a particular physical form and especially one that is allotropic, isomeric, or stereoisomeric (as in ƍ-benzene hexachloride)

2

: fourth in position in the structure of an organic molecule from a particular group or atom

also : having a structure characterized by such a position

ƍ-hydroxy acids

ƍ-lactones

Geographical Definition

Delta

geographical name

Del·​ta ˈdel-tə 

1

municipality south and southeast of Vancouver in southwestern British Columbia, Canada population 99,863

2

see delta, the