Collet

noun

1. A band, flange, ferrule, or collar, designed to grip and hold a tool or a workpiece under proper control, and usually to release it under control thereafter; such a collet usually is made of a hard, springy material, especially a metal.

   "That collet can handle up to 3/8-inch bits."

2. In jewelry, the rim (of a ring) within which a jewel is set. Compare bezel.

   "There is an almost invisible collet that secures the stone to the ring."

3. In an embryonic plant, the transition zone between the root and the hypocotyl (not clearly distinguishable in most plants.)

   "Collar rot forms in the collet between the stem and the root."