Definition of "concavity" [con•cav•i•ty]

• The state of being curved like the inner surface of a sphere. (noun)
• A surface or structure configured in such a curve: "a perfect concavity of white sand lined with palm . . . trees” ( Islands). (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The central part of the posterior surface presents a deep concavity which is moulded on the vertebral column and crura of the diaphragm."
• "On its upper side is seen a concavity which is produced by the section of the groove which runs along the convex and exterior (here upper) side of each branchial arch. ba, branchial artery in section, giving off the gill arteries (ga) to the adjacent sides of the gill leaflets, whence the blood is distributed in the leaflets; gv, the gill veins which run along the outer side of the gill leaflets, collecting the blood from them by minute veins and pouring it into bv, the branchial vein, which runs up the groove of the branchial arch and has the branchial artery superficial and exterior to it."
• "The play of concavity and convexity is announced by a pair of Tanktotems, watchful, hieratic personages built out of slender, vertical steel components and sliced tank ends."