— triadic , adj. — triadism , n.
/truy"ad, -euhd/ , n.
1. a group of three, esp. of three closely related persons or things.
2. Chem.
a. an element, atom, or group having a valence of three. Cf. monad (def. 2), dyad (def. 3).
b. a group of three closely related compounds or elements, as isomers or halides.
3. Music. a chord of three tones, esp. one consisting of a given tone with its major or minor third and its perfect, augmented, or diminished fifth.
4. ( cap. ) Mil. the three categories of strategic-nuclear-weapons delivery systems: bombers, land-based missiles, and missile-firing submarines.
[ 1540-50; triad- (s. of trias ) triás See TRI-, -AD 1 ]