Ineffabilis, & hoc ineffabile, pe. cor. Plin. That can not be spokē or vrtered: vnspeakeable: such as neyther hart can think nor pā descriue.Verba inesfabilia, Plin.Wordes that cannot bee pronounced.Nomina maximè ineffabilia. Plin.
Lewis and Short: Latin dictionary
ĭn-effābĭlis, e, adj., 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.