From an old Scottish word, "kythe," meaning "to make visible." Madeleine L'Engle used it to describe a fictional type of communication, in a sense like telepathy, a sort of wordless, mind to mind communication in which one person, in essence, almost becomes another, seeing through their eyes and feeling through their senses.
In such a frame of mind, the two people intuitively know the meaning of what the other is telling them, disregarding such things as words or pictures. The idea may be based on the concept of Oneness, which states that all that exists, is one in its source and end. Apparently, recollection and assertion of that concept puts a person "in Kythe" with that which they are concentrating on. (Wikipedia)