Using a smooth, curved arch of a sitting person to pound against with one's tool (various possibilities). Using a smooth, curved, blunt instrument to pound the soles of a young girl's feet into a doughy pulp, crushing and pulverizing as many bones as possible to prevent reformation into some other fixed shape, and to prevent bone splinters from protruding when the foot is placed into service.
　FOOT binding was:「…the custom of applying painfully tight binding to the feet of young girls to prevent further growth…in tiny feet, with the ideal length, called the 'Golden Lotus,' being about 7 cm (2.75 inches) long. …The process was started before the arch of the foot had a chance to develop fully, usually between the ages of 2 and 5. …To enable the size of the feet to be reduced, the toes on each foot were curled under, then pressed with great force downwards and squeezed into the sole of the foot until the toes broke. The broken toes were held tightly against the sole of the foot while the foot was then drawn down straight with the leg and the arch forcibly broken. The bandages were repeatedly wound in a figure-eight movement, starting at the inside of the foot at the instep, then carried over the toes, under the foot, and around the heel, the freshly broken toes being pressed tightly into the sole of the foot. At each pass around the foot, the binding cloth was tightened, pulling the ball of the foot and the heel together, causing the broken foot to fold at the arch, and pressing the toes underneath. …At the beginning of the binding, many of the foot bones would remain broken, often for years. However, as the girl grew older, the bones would begin to heal. Even after the foot bones had healed, they were prone to re-breaking repeatedly, especially when the girl was in her teenage years and her feet were still soft. …Qing Dynasty sex manuals listed 48 different ways of playing with women's bound feet.」
　　[　https://en.wikipedia.org/wiki/Foot_binding 2012-12-17　]　

Modern definitions (that generally disregard history) …excluding politically incorrect concepts and other meanings deemed offensive today; may list only pigeonholed definitions, euphemisms, or meaningless mnemonics)
Unihan extended: smooth and curved, to strike or beat heavily