- [Christian Theol] The union of three persons (the Father, the Son, and the Holy Ghost) in one Godhead, so that all the three are one God as to substance, but three persons as to individuality.
- Any union of three in one; three units treated as one; a triad, as the Hindu trinity, or Trimurti.
- Any symbol of the Trinity employed in Christian art, especially the triangle.
Etymology: OE. trinitee, F. trinité, L. trinitas, fr. trini three each. See Trinal