From a (as a negative particle) and the same as rhetos; unsaid, i.e. (by implication) inexpressible -- unspeakable.
see GREEK a
see GREEK rhetos
a. unsaid, unspoken: Homer, Odyssey 14, 466, and often in Attic.
b. unspeakable (on account of its sacredness) (Herodotus 5, 83, and often in other writings): 2 Corinthians 12:4, explained by what follows: ἅ οὐκ ἐξόν ἀνθρώπῳ λαλῆσαι.