Delta (upper case Δ, lower case δ) is the fourth letter of the Greek alphabet. In the system of Greek numerals it has a value of 4.
A river delta is named after the letter delta because it has roughly the triangular shape of the upper-case delta.
The upper-case letter Δ is used as the symbol for:
The lower-case letter δ is used as the symbol for:
Letters that arose from Delta include the Roman D and the Cyrillic letter Д.
The concept of the delta may perhaps be clarified by further exposition. Webster furnishes the following definition: (1) Delta is the name of the fourth letter of the Greek alphabet (equivalent to the English D) from the Phoenician name for the corresponding letter. The Greeks called the alluvial deposit at the mouth of the Nile, from its shape, the Delta of the Nile. (2) A tract of land shaped like the letter "delta," especially when the land is alluvial, and enclosed within two or more mouths of a river, as the Delta of the Ganges, of the Nile, of the Mississippi" .
Fingerprint Delta, John Edgar Hoover, FBI, The Science of Fingerprints Classification and Uses
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