Tether
late Middle English: from Old Norse tjóthr, from a Germanic base meaning ‘fasten’.
wiktionary
From Middle English tether, teder, from Old English *tēoder and/or Old Norse tjóðr ( > Danish tøjr); both from Proto-Germanic *teudrą(“rope; cord; shaft”), of uncertain origin. Perhaps from Proto-Indo-European *dewtro-, from Proto-Indo-European *dew-(“to tie”), or from Proto-Indo-European *dewk-(“to pull”). Cognate with North German Tüder(“tether for binding the cattle”).
etymonline
tether (n.)
late 14c., "rope for fastening an animal," not found in Old English, probably from a Scandinavian source akin to Old Norse tjoðr "tether," from Proto-Germanic *teudran (source also of Danish tøir, Old Swedish tiuther, Swedish tjuder, Old Frisian tiader, Middle Dutch tuder, Dutch tuier "line, rope," Old High German zeotar "pole of a cart"), from PIE root *deu- "to fasten" + instrumentive suffix *-tro-. Figurative sense of "measure of one's limitations" is attested from 1570s.
tether (v.)
late 14c. (implied in tethering), "confine by a tether," originally of grazing animals, from tether (n.). Figurative use also from late 14c. Related: Tethered.
