Triad

1. n. An element or radical whose valence is three.
2. n. A union of three; three objects treated as one; a ternary; a trinity; as, a triad of deities.
3. n. A chord of three notes.
4. n. The common chord, consisting of a tone with its third and fifth, with or without the octave.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.