Both a verb and a noun, tether keeps things tied together, or is the tie itself. Remember, when you tether that chair to those balloons, use a strong tether. You don't want to drop from the sky because you tied them together using a cheap piece of rope.
Think of the childhood game tether-ball. The ball is tethered to a pole by a tether. Tether usually refers to a rope or a chain, but it can also refer to an invisible bond or link. For example, the Internet can serve as a tether that links you to your pen pal in Germany. The love between a mother and her child keeps them tethered to each other for a lifetime. And whenever astronauts go for jaunts outside the space station, they tether themselves to the station using wires and a hook.