Tether Language: jargon: sailing A short length of line used to raise the tack of a sail. A short length of line connecting a sailor'sharness to the boat. Often clipped (with a carabiner-type connector) to jacklines to allow limited mobility. Any short line or cable used to limit a range of travel. v. At the end of my tether": reaching the end of one's endurance. In order to improve the lead of sheets to a sail, or to position it optimally (for example, a very high-cut yankeetopsailjib set flying from a topmast), or even simply to get the foot above the pulpit and lifelines a short length of line might be used between the sail's tack and the deckfitting. Often the line is made up with two shackles attached with splicedeyes.