Lewis Short
(adjective) : ĭn-effābĭlis, e
* Unutterable, unpronounceable (Plinian): nomina,Plin. 5 praef. § 1: verba,id. 28, 2, 4, § 20.— Adv.: ĭneffābĭlĭter, unutterably, ineffably (late Lat.): Deus ineffabiliter artifex,Aug. Enchir. 89.
Charlton T. Lewis, Charles Short, A Latin Dictionary