triad

Etymology

PIE word *tréyes From Latin triad-, stem of trias (“three, triad”), from Ancient Greek τριάς (triás). Sense 3 (“branch of a Chinese underground criminal society”) is due to the word being applied by the British authorities to underground society in Hong Kong based on the geometry of the Chinese character, derived from a name used by some of those societies, 三合會／三合会 (sānhéhuì, “Three Harmonies Society”), referring to the union between heaven, earth, and humanity.

noun

1. A grouping of three.
   There are, says the Irish triad, 'three fewnesses that are better than plenty: a fewness of fine words; a fewness of cows on grass; a fewness of good friends around good ale'. As an Ulsterman I would agree. 2000, David Pierce, Irish Writing in the Twentieth Century: A Reader, page 625
2. A word of three syllables.
   In his general deportment he was pompous and important, affecting a species of florid elocution, which often became ridiculous from his misarranging the triads and quaternions with which he loaded his sentences. 1815, Sir Walter Scott, chapter 13, in Guy Mannering
3. A branch of a Chinese underground criminal society, mostly based in Hong Kong.
   The point — and the symbolism — was that so long as the informer kept his mouth shut he was alive. Harry had seen the result of zjuk carried out by the Tapei Triad on a poor jerk they found in a back street of Tan-shui. They had used broad nail heads that didn’t make such big holes on their way in. When the paramedics came and pulled the brick off the dead man, the face came with it. 2012 [2011], Jo Nesbø, translated by Don Bartlett, Gjenferd [Phantom] (Fiction), New York: Alfred A. Knopf, →LCCN, →OCLC, page 99
4. (electronics) on a CRT display, a group of three neighbouring phosphor dots, coloured green, red, and blue.
5. (music) A chord consisting of a root tone, the tone two degrees higher, and the tone four degrees higher in a given scale.