# delta

Pronunciation: say "DEL-tuh" /ˈdɛltə/

## Noun

1. A landform at the mouth of a river, where the river empties into a body of water such as a sea or lake.
   - Simple: The land at the end of a river, where the river flows into a sea, a lake, or other water.
   - _The river splits into dozens of channels as it crosses the delta to the gulf._
   - _Rising seas threaten the farms and villages of the Nile Delta._
2. The fourth letter of the modern Greek alphabet, written Δ as a capital and δ in lowercase.
   - Simple: The fourth letter of the Greek alphabet, written Δ or δ.
   - _The fraternity's sign shows a large delta between two other Greek letters._
   - _In the Greek alphabet, delta comes after gamma and before epsilon._
3. The symbol Δ, or the change in a quantity that the symbol stands for.
   - Simple: The math sign Δ, or how much an amount has changed.
   - _The engineers measured the pressure delta across the valve every hour._
   - _A large delta between indoor and outdoor temperatures drives heat through the walls._
4. Ellipsis of delta variant, a variant of the SARS-CoV-2 virus. — Ellipsis of delta variant (variant of the SARS-CoV-2 virus).
   - Simple: Short for delta variant. It is a form of the virus that causes COVID-19.
   - _Hospitals filled up again as delta spread through communities with low vaccination rates._
   - _Researchers compared how easily delta and earlier variants passed between members of a household._
5. Alternative letter-case form of Delta from the NATO/ICAO Phonetic Alphabet.
   - Simple: Alternative letter-case form of Delta from the NATO/ICAO Phonetic Alphabet. It is the code word for the letter D.
   - _The caller read out the license plate as delta, echo, four, seven._
   - _Ground control cleared the jet to taxi via delta to the main runway._
6. The full set of differences between two versions of the same file.
   - Simple: A list of all the changes between an old and a new copy of a file.
   - _Instead of copying the whole database each night, the backup tool keeps a series of deltas._
   - _Reading the delta line by line, he spotted a typo in the new configuration._
7. The rate at which an option's value changes in relation to changes in the price of the underlying asset.
   - Simple: How much an option's value moves when the price of the asset it is based on moves.
   - _With a delta of 0.5, the call option should gain about fifty cents for every dollar the stock rises._
   - _Market makers adjust their stock holdings throughout the day to keep their portfolio's delta in check._
8. An effect that is small but large enough to notice. *(colloquial)*
   - Simple: A small effect that you can still notice.
   - _Moving the check out of the loop improved performance by delta, enough to show up in the benchmarks._
   - _The patch raises memory use by delta, so we flagged it in the release notes._
10. The closed figure made by joining three coils or circuits end to end in sequence, especially in a three-phase system.
   - Simple: A closed shape made by joining three electric coils or circuits, one after another, end to end.
   - _The transformer's primary windings are connected in delta, while the secondary windings use a wye arrangement._
   - _The technician traced the fault to a burned-out section of the generator's delta winding._
11. A star typically surpassed in brightness by only three others in its constellation.
   - Simple: A star that is usually the fourth brightest in its group of stars.
   - _Astronomers tracked the brightness of the constellation's delta over several nights._
   - _Unlike most deltas, this star outshines the gamma of its constellation._
12. In the US Space Force, a unit nominally headed by a colonel, equivalent to an Air Force operations wing or an army regiment. *(dialectal, Space Force, US)*
   - Simple: A unit of the US Space Force, officially led by a colonel, at the same level as an army regiment.
   - _After the reorganization, the base's squadrons were grouped under a single delta._
   - _Officers from three deltas met to coordinate support for the satellite launch._
13. A cargo bike with a single wheel in front and two wheels at the back.
   - Simple: A bike for carrying loads that has one wheel at the front and two at the back.
   - _The courier traded her two-wheeler for a delta, which keeps heavy crates steady over the rear axle._
   - _Deltas are easier to balance at low speed than two-wheeled cargo bikes, but they take up more room on a bike path._
14. A value given in delta notation that expresses the relative abundances of isotopes.
   - Simple: A number scientists use to compare how much there is of different forms of the same element.
   - _The oxygen-isotope deltas of the fossil shells shift sharply at the boundary between the two layers._
   - _Each sample's carbon delta was reported relative to the international reference standard._
15. Any of the four baryons made of up and down quarks with a combined spin of 3/2, written Δ⁺⁺, Δ⁺, Δ⁰ and Δ⁻.
   - Simple: Any of four very small particles made of three up or down quarks, with a total spin of 3/2.
   - _When a pion strikes a proton at the right energy, the pair can briefly form a delta that decays almost at once._
   - _The four deltas carry electric charges ranging from plus two down to minus one._
16. The angle formed at the center of a circle by lines drawn to the two ends of a circular arc.
   - Simple: The angle at the center of a circle between lines drawn to the two ends of a curved section.
   - _With the radius and the delta known, the crew could calculate the length of the curve._
   - _The plans list a delta of 32 degrees for the curve on the bridge approach._

## Verb

9. To compare two versions of a file to find where they differ, which shows where a programmer has made edits.
   - Simple: To compare an old and a new copy of a file to find what someone changed.
   - _The build script deltas each source file against the last release before packaging the update._
   - _Developers delta the configuration files after every merge to catch accidental edits._
17. In cryptanalysis, to compute how each character of an enciphered text differs from the character a fixed number of places earlier.
   - Simple: To work out how each letter in a coded message differs from one a set number of places before it.
   - _Analysts would delta the intercepted stream so that regularities in the machine's wheels showed through._
   - _Working by hand, the team deltaed each new intercept and tallied the results on squared paper._

## Origin

From Ancient Greek δέλτα (délta), borrowed from a Phoenician word for "door" and ultimately from Proto-Semitic *dalt-; it is a doublet of dalet. The river sense comes from the triangular shape of the capital Greek letter Δ, and the USSF sense from the delta wing, the force's symbol, a triangular wing shaped like Δ.

Source: DictionaryAI, https://dictionaryai.com/define/delta (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).