triplicity

Triplicity refers to a group or set of three, or the state of being threefold.

The word appears most often in astrology, where it denotes any of the four groups of three zodiac signs that share the same element: fire signs (Aries, Leo, Sagittarius), earth signs, air signs, and water signs.

The fire triplicity is associated with passion and energy.

Outside astrology, triplicity can describe any arrangement or concept involving three related parts, though this usage is uncommon and somewhat literary.