Word Origin and History for at the end ones tether
late 14c., "rope for fastening an animal," probably from O.N. tjoðr "tether," from P.Gmc. *teudran (cf. Dan. tøir, Swed. tjuder, O.Fris. tiader, M.Du. tuder, Du. tuier "line, rope," O.H.G. zeotar "pole of a cart"), from PIE base *deu- "to fasten" + instrumentive suffix *-tro-. Figurative sense of "measure of one's limitations" is attested from 1570s. The verb is first recorded late 15c., from the noun.