# Delta (letter)

Delta (letter)

Delta (uppercase Δ, lowercase δ; δέλτα; Modern Greek [ˈðelta] dhélta) is the fourth letter of the Greek alphabet. In the system of Greek numerals it has a value of 4. It was derived from the Phoenician letter Dalet. Letters that come from delta include Latin D and Cyrillic Д.

A river delta (originally, the Nile River delta) is so named because its shape approximates the upper-case letter delta (the shape is a triangle).  The alphabet on a black figure vessel, with a D-shaped delta.

## Pronunciation

In Ancient Greek, it represented a voiced dental plosive /d/. In Modern Greek, it represents a voiced dental fricative /ð/, like the "th" in "that" or "this". It is romanized as d or dh.

## Mathematics and the Sciences

### Upper case

The upper-case letter Δ can be used to denote

• Change of any variable quantity, in mathematics and the sciences; for example, in ${y_2-y_1\over x_2-x_1} = {\Delta y \over \Delta x}$, the average change of y per unit x, i.e. the change of y over the change of x $\Delta f = \sum_{i=1}^n {\frac{\partial^2 f}{\partial x_i^2}}$ $\Delta = b^2 - 4ac\,\!$
• A macroscopic change in the value of a variable in mathematics or science
• Uncertainty in a physical variable as seen in for instance the uncertainty principle
• An interval of possible values for a given quantity for instance across a sample[citation needed]
• Any of the delta particles in particle physics
• The determinant of the matrix of coefficients of a set of linear equations (see Cramer's Rule)
• That an associated locant number represents the location of a covalent bond in an organic compound, the position of which is variant between isomeric forms
• In chemistry, it is often used to represent the addition of heat in a reaction.
• In legal shorthand, it represents a defendant
• In the financial markets, it is one of the Greeks that describes the rate of change of an option price for a given change in the underlying benchmark
• It is the symbol of the Greek inventor and architect Daedalus
• In genetics, it can stand for a gene deletion, e.g. the CCR5-Δ32 a deletion of the CCR5 at the 32nd base pair segment
• The American Dental Association cites it (together with omicron for "odont") as the symbol of dentistry.

### Lower case

The lower-case letter δ can be used to denote

### Meteorology

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### Look at other dictionaries:

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• Delta — Del ta, n.; pl. {Deltas}. [Gr. de lta, the name of the fourth letter of the Greek alphabet (the capital form of which is [Delta], Eng. D), from the Ph[oe]nician name of the corresponding letter. The Greeks called the alluvial deposit at the mouth …   The Collaborative International Dictionary of English

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