biconcave

adj biconcave

• dipped — to plunge (something, as a cloth or sponge) temporarily into a liquid, so as to moisten it, dye it, or cause it to take up some of the liquid: He dipped the brush into the paint bucket.
• hollow — having a space or cavity inside; not solid; empty: a hollow sphere.
• round — having a flat, circular surface, as a disk.
• rounded — having a flat, circular surface, as a disk.
• sinking — to displace part of the volume of a supporting substance or object and become totally or partially submerged or enveloped; fall or descend into or below the surface or to the bottom (often followed by in or into): The battleship sank within two hours. His foot sank in the mud. Her head sinks into the pillows.