Lewis & Short

trīnĭtas, ātis, f. [trini], the number three, a triad (post-class.).

  1. I. In gen.: facta exinde trinitas generum est ex trinitate causarum, Tert. adv. Val. 17.
  2. II. In partic., the Trinity, Tert. adv. Prax. 3; Cod. Just. 1, 1, 1.