Curved like the inner surface of a sphere. (adjective)
A concave surface, structure, or line. (noun)
To make concave. (verb-transitive)
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.
Use "concave" in a sentence
"It flowed in a gentle concave from the road up the mountain, its farther boundary an unbroken line of timber."
"The last three types, called concave lenses, scatter parallel rays so that they do not come to a focus, but diverge widely after passage through the lens."
"That surface of the bow which faces the string when drawn into action, that is, the concave arc, is called the belly of the bow."