Plane or flat on one side, and concave on the other. See lens.(adjective)
Gnu Collaboartive International Dictionary of English: licensed under The Code Project Open License (CPOL)
Use "plano-concave" in a sentence
"Galileo's telescope consisted of two lenses -- one plano-convex, the other plano-concave, the latter being held next the eye."
"There, two lenses were made, one plano-convex, and the other plano-concave, and these were placed in a tube made of sheet copper."
"Every part of the immense observatory and of the telescope is of American production, with the single important exception of the cast glass disc from which the two principal lenses, the one double convex and the other plano-concave, are produced."