Indeclarable

It is uncomprehensible, unsearchable, and indeclarable.

Source: wiktionary

For the true mercy of God, although it had available an indeclarable number of ways to restore the human race, chose this way as best of all, in which, for the destruction of the Devil's work, use would be made not of the strength of power but of the claims of justice.

Source: wiktionary

It was a means of declaring the otherwise indeclarable, a method of externalizing and temporarily reconciling that highly unstable, even volatile, sexual difference that was felt within but not understood.

Source: wiktionary