"I wrote many novels which … contained the element of the projected collective unconscious, which made them simply incomprehensible to anyone who read them, because they required the reader to accept my premise that each of us lives in a unique world."
- Philip K. Dick

Robert Heinlein liked this term enough that he used it in his classic 1941 novel Methuselah's Children:

Had there been a bystander, he would have been startled to observe what appeared to be a standard Camden rise up off the ground as easily as a skycar. He would not have long to wonder - the car moved out over the lake, dropped down to the water and sank beneath it. Seventeen minutes later, the car rose up to the surface of a small pool of water, a pool that occupied much of the floor of an artificial cavern.

This term also appears in The Swordsman of Sarvon (1932) by Charles Cloukey:

The little skycar maintained its headlong rush for almost two hours. Then it circled down to land upon the wide ledge half-way up the cliff-side, the ledge upon which the cave opened.