Shackle

noun

1. (usually in the plural) A restraint fit over a human or animal appendage, such as a wrist, ankle or finger; normally used in pairs joined by a chain.

   "The prisoner lay in shackles in his gloomy cell."

2. A U-shaped piece of metal secured with a pin or bolt across the opening, or a hinged metal loop secured with a quick-release locking pin mechanism.
3. (usually in the plural) A restraint on one's action, activity, or progress.
4. A fetter-like band worn as an ornament.
5. A link for connecting railroad cars; a drawlink or draglink.