our minister always referred to the Father, the Son and the holy Spigot

Daddy-O, Junior, and Spook

And on the more general subject of triads:
the three Furies: Tisiphone (avenger of murder), Megaera (the jealous one), and Alecto (unceasing in anger).
the three judges of the Underworld: Minos, Rhadamanthus, and Aeacus.
the three witches of Macbeth
the Olympic motto: Citius, altius, fortius ("faster, higher, stronger")