Kything is derived from the Old English kythe, cýðe; a word known from both The Vespasian Psalter (c.825) and the West Saxon Gospels (c.1025). Meaning "to announce, proclaim, declare, tell, to make known in words, to manifest, to make visible", it survived as the Scottish dialect word kythe.
The author Madeleine L'Engle used the word kythe to describe a fictional type of communication, in a sense like telepathy, found in several of the books in her Time Quintet. L'Engle reportedly discovered the term in "an old Scottish dictionary" belonging to her grandfather.
In the Time Qintet books, Kything is 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.
Kything is portrayed as a way to be present with others without regard to space, time, or relative size. Through kything, humans can be together inside a subcellular mitochondrion, as seen in A Wind in the Door, or in communication despite being centuries apart, as seen in A Swiftly Tilting Planet.
Characters depicted as kything include Charles Wallace Murry (for whom it comes naturally), Meg Murry and Calvin O'Keefe. Meg and Calvin share a particular bond with each other, part of their growing relationship which eventually leads to marriage. Meg also spends much of A Swiftly Tilting Planet kything with her brother, Charles Wallace, thus experiencing vicariously his travels in time while supporting his efforts with research and prayer.
Catholic priest Louis M. Savary and Patricia H. Berne have created a handbook for kything as a spiritual practice, in Kything: The Art of Spiritual Presence.