The corresponding word in Greek is tριάς, meaning "a set of three" or "the number three" [REF].
Tertullian, a Latin theologian who wrote in the early 3rd century, is credited as being the first to use the Latin words "Trinity",[REF] "person" and "substance"[REF] to explain that the Father, Son, and Holy Spirit are "one in essence-not one in Person" [REF].