trinity (n.) Look up trinity at Dictionary.com
early 13c., "the Father, Son and Holy Spirit," constituting one God in prevailing Christian doctrine, from Old French trinite (11c.), from Latin trinitatem (nominative trinitas) "Trinity, triad" (Tertullian), from trinus "threefold, triple," from plural of trini "three at a time, threefold," related to tres (neuter tria) "three." The Latin word was widely borrowed in European languages with the rise of Christianity (e.g. Irish trionnoid, Welsh trindod, German trinität).