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triad

[trahy-ad, -uh d] /ˈtraɪ æd, -əd/
noun
1.
a group of three, especially of three closely related persons or things.
2.
Chemistry.
  1. an element, atom, or group having a valence of three.
    Compare monad (def 2), dyad (def 3).
  2. a group of three closely related compounds or elements, as isomers or halides.
3.
Music. a chord of three tones, especially one consisting of a given tone with its major or minor third and its perfect, augmented, or diminished fifth.
4.
(initial capital letter) Military. the three categories of strategic-nuclear-weapons delivery systems: bombers, land-based missiles, and missile-firing submarines.
Origin
1540-1550
1540-50; < Latin triad- (stem of trias) < Greek triás See tri-, -ad1
Related forms
triadic, adjective
triadism, noun
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Examples from the web for triadic
  • These inventions are called triadic patent families.
British Dictionary definitions for triadic

triad

/ˈtraɪæd/
noun
1.
a group of three; trio
2.
(chem) an atom, element, group, or ion that has a valency of three
3.
(music) a three-note chord consisting of a note and the third and fifth above it
4.
an aphoristic literary form used in medieval Welsh and Irish literature
5.
the US strategic nuclear force, consisting of intercontinental ballistic missiles, submarine-launched ballistic missiles, and bombers
Derived Forms
triadic, adjective
triadism, noun
Word Origin
C16: from Late Latin trias, from Greek; related to Greek treis three

Triad

/ˈtraɪæd/
noun
1.
any of several Chinese secret societies, esp one involved in criminal activities, such as drug trafficking
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for triadic

triad

n.

1540s, "group or set of three," from Late Latin trias (genitive triadis), from Greek trias (genitive triados), from treis "three" (see three). Musical sense of "chord of three notes" is from 1801.

Online Etymology Dictionary, © 2010 Douglas Harper
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triadic in Medicine

triad tri·ad (trī'ād', -əd)
n.

  1. A collection of three things or symptoms having something in common.

  2. The transverse tubule, and the terminal cisternae on each side of it, in a skeletal muscle fiber.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Encyclopedia Article for triadic

triad

in chemistry, any of several sets of three chemically similar elements, the atomic weight of one of which is approximately equal to the mean of the atomic weights of the other two. Such triads-including chlorine-bromine-iodine, calcium-strontium-barium, and sulfur-selenium-tellurium-were noted by the German chemist J.W. Dobereiner between 1817 and 1829. The triad was the earliest atomic-weight classification of the elements

Learn more about triad with a free trial on Britannica.com
Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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10
11
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