means A rope, chain, or cord that ties an animal or object to a fixed point so it can only move within a limited range, or by extension any constraint that keeps something or someone from straying.

from From Middle English 'tethir,' likely borrowed from Old Norse 'tjóðr,' meaning a rope for fastening grazing animals — a word that came over with the Norse and stuck around the pasture. It has Germanic cousins, like the Old High German 'zeotar,' and the whole family seems to point back to a root about binding or fastening. The figurative 'end of one's tether' — the point where the rope runs out and there's no more give — keeps the grazing-goat image alive in everyday despair.