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

Examples of delta in a Sentence

Recent Examples on the Web

Noun

The tunnel would siphon relatively fresh Sacramento River water at the north end of the delta and deliver it to facilities at the more brackish south end. —George Skelton, Los Angeles Times, 9 June 2025

Coogler drew from vampire lore and a beloved great uncle’s passion for delta blues music to draw the lines between the Black American experience, past, present, and future in Sinners, set on one sweltering 1932 day in Clarksdale, Mississippi. —Mankaprr Conteh, Rolling Stone, 2 June 2025

However, this the kind of performance delta that changes how design teams think about iteration cycles, performance optimization, feature integration, verification and validation, and any number of time-sensitive steps. —Dave Altavilla, Forbes.com, 12 May 2025

His forthcoming book ventures to Ecuadorian cloud forests, the deltas of Southeastern India and the forests of eastern Quebec to explore the critical fight worldwide to protect our waterways. —American Booksellers Association, USA Today, 10 May 2025

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

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