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

As Daniel notes, the longer first stint on the inverse tire strategy didn’t pay off to try and close the gap with a tire delta late on, as the race’s low tire degradation significantly reduced this possibility. —Luke Smith, New York Times, 9 Apr. 2025

Many rivers have natural bifurcations, where the branch later returns to the main river after some distance, such as a braided river or delta. —Newsweek Staff, MSNBC Newsweek, 4 Apr. 2025

Now, the delta is only around 1% for each category, but the universality is interesting. —Gary Drenik, Forbes.com, 2 Apr. 2025

In this case, the delta of the downside put is -.2, and the absolute value is .2 or 20%. —Michael Khouw, CNBC, 31 Mar. 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