The verb tense of the word knowledge which is the third element in the series or table; data, information, knowledge, wisdom. About as far as a couple of truthiness types can claim to have gotten aside from the wise who wonder why.
"There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know." - Donald Rumsfeld
What about unknown knowns? It has to be symmetrical like +ve and -ve.