tether

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A rope, chain, strap, or cord for keeping an animal within a certain radius.
• noun A similar ropelike restraint used as a safety measure, as for a young child or an astronaut outside a spacecraft.
• noun A rope, chain, cable, or other line for restraining or securing an object.
• noun The extent or limit of one's resources, abilities, or endurance.
• noun A range of allowable behavior or responsibility.
• transitive verb To restrain or secure with a tether.

from The Century Dictionary.

• noun A rope, chain, or halter, especially one by which a grazing animal is confined within certain limits: often used figuratively, in the sense of a course in which one may move until checked; scope allowed.
• To confine, as a grazing animal, with a rope or chain within certain limits; hence, to tie (anything) with or as with a rope or halter.

from the GNU version of the Collaborative International Dictionary of English.

• noun A long rope or chain by which an animal is fastened, as to a stake, so that it can range or feed only within certain limits.
• transitive verb To confine, as an animal, with a long rope or chain, as for feeding within certain limits.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a rope, cable etc. that holds something in place whilst allowing some movement
• noun by extension the limit of one's abilities, resources etc
• noun dialect The cardinal number three in an old counting system used in Teesdale and Swaledale. (Variant of tethera)
• verb to restrict something with a tether

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun restraint consisting of a rope (or light chain) used to restrain an animal
• verb tie with a tether