triad

noun

1. A grouping of three.

   “Later artworks showed many animals and gods, some of which were clearly identified with heavenly body. They often included the symbolic triad of Sun, Moon, and Venus.”

   “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.”

2. A grouping of three.
3. 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.”

4. 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.”

5. On a CRT display, a group of three neighbouring phosphor dots, coloured green, red, and blue.
6. A chord consisting of a root tone, the tone two degrees higher, and the tone four degrees higher in a given scale OR any chord with three notes.