plural deltas
1
: the 4th letter of the Greek alphabet see Alphabet Table
2
: something shaped like a capital Greek 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)
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
Suresh V. Kuchipudi
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 4communications code word
—used as a code word for the letter d
: of, relating to, or characteristic of the The Delta region of Mississippi
Examples of delta in a Sentence
Recent Examples on the Web
Ryan Fonseca, Los Angeles Times, 3 Oct. 2024
But the river’s final 106 kilometers flow through Mexico to a delta along the Gulf of Baja California.
—Byroberto González, science.org, 14 Aug. 2024
The Perseverance team noticed and targeted the rock in late June as the rover was trundling across the northern slope of Neretva Vallis, a half-kilometer-wide channel carved out eons ago by a river rushing into Jezero Crater, which once held a large lake and delta system.
—Lee Billings, Scientific American, 26 July 2024
In the delta era, the rate of long COVID among the unvaccinated fell slightly to 9.51 out of 100.
—Beth Mole, Ars Technica, 18 July 2024
See all Example Sentences for delta 
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Noun
What else is going on A decision to reduce water flows in California’s delta sparked a debate over an imperiled fish.
—Ryan Fonseca, Los Angeles Times, 3 Oct. 2024
But the river’s final 106 kilometers flow through Mexico to a delta along the Gulf of Baja California.
—Byroberto González, science.org, 14 Aug. 2024
The Perseverance team noticed and targeted the rock in late June as the rover was trundling across the northern slope of Neretva Vallis, a half-kilometer-wide channel carved out eons ago by a river rushing into Jezero Crater, which once held a large lake and delta system.
—Lee Billings, Scientific American, 26 July 2024
In the delta era, the rate of long COVID among the unvaccinated fell slightly to 9.51 out of 100.
—Beth Mole, Ars Technica, 18 July 2024
See all Example Sentences for delta
Dictionary Entries Near delta
Cite this Entry
“Delta.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/delta. Accessed 26 Nov. 2024.
Copy CitationMedical 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
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
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