undefinableness

My deepest hope was in the undefinableness of its object: I knew only that a clear idea (and Plato says all clear ideas are true) of the subtile susceptibilities of nitrate of silver,

The Atlantic Monthly, Volume 10, No. 58, August, 1862 Various

In spite of this doctrine's untenableness (because by then that definition, overrepeatedly pretended unachievable, had in fact long been objectively found), the doctrine of the objective undefinableness of

Citizendium, the Citizens' Compendium - Recent changes [en] 2008