The pit was a saucer-shaped concave, naturally formed, with a top diameter of about thirty feet, and shallow enough to allow the sunshine to reach their heads.
A heavy unbroken crust of cloud stretched across the sky, shutting out every speck of heaven; and a distant halo which hung over the town of Casterbridge was visible against the black concave, the luminosity appearing the brighter by its great contrast with the circumscribing darkness.
This, however, could not be helped; she would not, on any consideration, treat Boldwood harshly, having once already ill-used him, and the moon having risen, and the gig being ready, she drove across the hilltop in the wending way’s which led downwards—to oblivious obscurity, as it seemed, for the moon and the hill it flooded with light were in appearance on a level, the rest of the world lying as a vast shady concave between them.
There are no more uses of "concave" in the book.
Show samples from other sources
Of what use is genius, if the organ is too convex or too concave and cannot find a focal distance within the actual horizon of human life?
Emerson, Ralph Waldo -- Essays, Second Series
He touched my head, which is our tradition, but my father was worried, as I had nothing but skin, no bone to protect my brain, and my head beneath the shawl was concave.