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c.1200, Greek letter shaped like a triangle, equivalent to our "D," the name from Phoenician daleth "tent door." Herodotus used it of the mouth of the Nile, and it was so used in English from 1550s; applied to other river mouths from 1790.
delta del·ta (děl'tə)
Symbol δ, Δ The fourth letter of the Greek alphabet.
The fourth one in a series.
A surface or part that resembles a triangle, such as the terminus of a pattern in a fingerprint or the shape of a muscle.
Of or characterizing the atom or radical group that is fourth in position from the functional group of atoms in an organic molecule.
Of or relating to one of four closely related chemical substances.
Relating to or characterizing a polypeptide chain that is one of five types of heavy chains present in immunoglobins.
A usually triangular mass of sediment, especially silt and sand, deposited at the mouth of a river. Deltas form when a river flows into a body of standing water, such as a sea or lake, and deposits large quantities of sediment. They are usually crossed by numerous streams and channels and have exposed as well as submerged areas.
1. A quantitative change, especially a small or incremental one (this use is general in physics and engineering). "I just doubled the speed of my program!" "What was the delta on program size?" "About 30 percent." (He doubled the speed of his program, but increased its size by only 30 percent.)
2. [Unix] A diff, especially a diff stored under the set of version-control tools called SCCS (Source Code Control System) or RCS (Revision Control System). See change management.
3. A small quantity, but not as small as epsilon. The jargon usage of delta and epsilon stems from the traditional use of these letters in mathematics for very small numerical quantities, particularly in "epsilon-delta" proofs in limit theory (as in the differential calculus). The term delta is often used, once epsilon has been mentioned, to mean a quantity that is slightly bigger than epsilon but still very small. "The cost isn't epsilon, but it's delta" means that the cost isn't totally negligible, but it is nevertheless very small. Common constructions include "within delta of ---", "within epsilon of ---": that is, "close to" and "even closer to".