the fourth letter of the greek alphabet (Δ, δ).
the consonant sound represented by this letter.
the fourth in a series of items.
anything triangular, like the Greek capital delta (Δ).
Mathematics. an incremental change in a variable, as Δ or δ.
a nearly flat plain of alluvial deposit between diverging branches of the mouth of a river, often, though not necessarily, triangular: the Nile delta.
(usually initial capital letter) a word used in communications to represent the letter D.
(initial capital letter) Astronomy. a star that is usually the fourth brightest of a constellation: The fourth brightest star in the Southern Cross is Delta Crucis.

1350–1400; Middle English deltha < Latin delta < Greek délta; akin to Hebrew dāleth

delta, estuary. Unabridged


noun Military.
the NATO name for a class of Soviet nuclear-powered ballistic missile submarine armed with 16 multi-warhead missiles. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
delta (ˈdɛltə)
1.  the fourth letter in the Greek alphabet (Δ, δ), a consonant transliterated as d
2.  an object resembling a capital delta in shape
3.  (capital when part of name) the flat alluvial area at the mouth of some rivers where the mainstream splits up into several distributaries: the Mississippi Delta
4.  maths a finite increment in a variable
[C16: via Latin from Greek, of Semitic origin; compare Hebrew dāleth]

Delta1 (ˈdɛltə)
1.  (foll by the genitive case of a specified constellation) usually the fourth brightest star in a constellation
2.  any of a group of US launch vehicles used to put unmanned satellites into orbit
3.  communications a code word for the letter d

Delta2 (ˈdɛltə)
a state of Nigeria, on the Niger river delta on the Gulf of Guinea. Capital: Asaba. Pop: 4 098 391 (2006). Area: 17 698 sq km (6833 sq miles)

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

c.1200, Gk. 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 Eng. from 1555; applied to other river mouths from 1790. Deltoid muscle so called since 1741, from its shape.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

delta del·ta (děl'tə)

  1. Symbol δ, Δ The fourth letter of the Greek alphabet.

  2. The fourth one in a series.

  3. A surface or part that resembles a triangle, such as the terminus of a pattern in a fingerprint or the shape of a muscle.

  1. Of or characterizing the atom or radical group that is fourth in position from the functional group of atoms in an organic molecule.

  2. Of or relating to one of four closely related chemical substances.

  3. Relating to or characterizing a polypeptide chain that is one of five types of heavy chains present in immunoglobins.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
delta   (děl'tə)  Pronunciation Key 
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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Computing Dictionary

Delta definition


1. An expression-based language developed by J.C. Cleaveland in 1978.
2. A string-processing language with single-character commands from Tandem Computers.
3. A language for system specification of simulation execution.
["System Description and the DELTA Language", E. Holback-Hansen et al, DELTA Proj Rep 4, Norweg Comput Ctr, Feb 1977].
4. A COBOL generating language produced by Delta Software Entwicklung GmbH (

delta definition

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".
[Jargon File]

The Free On-line Dictionary of Computing, © Denis Howe 2010
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Example sentences
But the greatest damage was in the low-lying delta.
At the river delta, the river-borne silt has fostered an extremely fertile
The final brainwave state is delta.
The delta between persuasion and proof is faith in their personal choice.
Images for delta
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