1The fourth letter of the Greek alphabet (Δ, δ), transliterated as ‘d’.‘Other symbols use in chemistry include the Greek letter delta to denote a change in energy levels and an arrow to indicate the direction a reaction proceeds in.’
- ‘Casey guessed the next would be delta: phonetic alphabet’
- ‘Apparently they don't teach you anything useful, just epsilons and deltas.’
- ‘It should be noted that the scaled necrosis depth, d / delta, also depends on the irradiation geometry and the incident light dose.’
- 1.1British A fourth-class mark given for an essay, examination paper, or other piece of work.
- 1.2as modifier The fourth in a series of items, categories, etc.‘delta hepatitis’
- ‘The study reports the influence of delta infection on the severity of hepatitis B.’
- ‘To me it looked like the alpha males on the rampage, and alpha males are always scary to all the gamma and delta males.’
- ‘Our results suggest that delta infection may not be very common in Indian patients with HBV-related liver diseases.’
- ‘Thus, our results suggest that delta co-infection is more common in acute liver diseases while delta super-infection occurs more frequently in chronic liver disease.’
- ‘For example, the babies are taught to be satisfied with their own caste of which there are five: alphas at the top, then betas, gammas, deltas, and epsilons at the bottom.’
- ‘Four changes occur in iron, which give rise to forms known as alpha, beta, gamma and delta.’
- 1.3Astronomy followed by Latin genitive The fourth (usually fourth-brightest) star in a constellation.‘Delta Cephei’
- ‘Other bright stars in Canis Major are Adhara (Epsilon Canis Majoris), Mirzam (Beta Canis Majoris), and Wezen (Delta Canis Majoris).’
- ‘As a connecting star to Pegasus, it is also known as Delta Pegasi, though this name is rarely used.’
2A code word representing the letter D, used in radio communication.
- ‘Pilot: Regina Tower, (this is) Cessna foxtrot bravo charlie delta (over).’
3A difference between two things or values.‘there's a delta between perception and reality’
- ‘as long as the price delta is not too great, consumers can be sold on specs and future-proofing’
- 3.1Computing A change or set of changes made to a file or program, especially as part of an update to a later version.‘this approach saves disk space by storing only data deltas’
- ‘updates will be delivered as delta updates instead of complete application downloads’
- ‘This is mock example.’
1(also δ, Δ)Mathematics
Variation of a variable or function.
2(also δ, Δ)Mathematics
A finite increment.
The discriminant of a quadratic equation.
Greek, from Phoenician daleth.
A triangular tract of sediment deposited at the mouth of a river, typically where it diverges into several outlets.‘the Nile delta’
- ‘a huge delta system developed’
- ‘It and many other old zircons come from metamorphosed sediments deposited in river deltas some 3 billion years ago in what is now southwestern Australia.’
- ‘Discriminating between deposits of tidally influenced deltas and tide-dominated coastal mud flats in the rock record is often difficult.’
- ‘Innumerable lagoons, lakes, canals, estuaries and the deltas of 44 rivers make up the 900 km of backwater network of the State.’
- ‘In time, as the Ecca Sea filled with sediment and the deltas prograded basinward, large tracts of river channels and floodplains emerged.’
- ‘The forests and estuaries of the delta also benefited from huge floods released into the river from behind dams during the El Niño years of the 1980s and 1990s.’
- ‘Water flow in the rivers decreased when the region's climate changed about 5,000 years ago and wind began to winnow the river delta's dried sediments.’
- ‘But those levees denied the delta replenishing river sediment, just as oil prospectors began to dredge coastal wetlands.’
- ‘They carry silt from the Mississippi River that replenishes the delta and keeps the coastland above the water line, creating a gradual buffer from the sea.’
- ‘These lead down to what appears to be a shoreline with river deltas and sand bars.’
- ‘As the rate of rising sea level gradually slowed, rivers began to build deltas from retreating shorelines into the encroaching seas.’
- ‘You can't save beaches and wetlands with seawalls, and you can't wall off river deltas and floodplains that contain much of the world's most productive agricultural land.’
- ‘Most Pamiri villages exist at the triangle of a river delta.’
- ‘The Teshekpuk area, a network of wet meadows, river deltas, coastal lagoons and small ponds, is the prime calving grounds for a 25,000-strong caribou herd.’
- ‘Erpetoichthys calabaricus is distributed solely in tropical Africa, where it occupies habitats ranging from flowing rivers to flood plains and internal river deltas.’
- ‘Irrigated rice agriculture is also practiced in numerous smaller river deltas and plains along the country's coast.’
- ‘The flows lead down to a shoreline which scientists think has river deltas and sandbars, all familiar geographical features from home.’
- ‘The minerals are deposited in lakes, deltas and meander further downstream, where they build up and form sedimentary rocks such as calcite, selenite, pyrite and dolomite.’
- ‘In Bangladesh, settlement of populations in high risk areas such as floodplains and river deltas increases vulnerability.’
- ‘Here in northern Idaho, near where the deluge began, I survey the rounded mountains and river deltas, trying to imagine the force of such a catastrophe.’
- ‘Long and narrow it stretches east to west along the Gambia River and the capital, Banjul, lies on an island in the river delta.’
Mid 16th century originally specifically as the Delta (of the River Nile), from the shape of the Greek letter (see delta).