Green’s Dictionary of Slang

Sir Tristram’s knot n.

the hangman’s noose.

1562

W. Bullein Bk of Simples Folio 27: Here is an herbe whiche light fellowes, merily will call Gallowgrasse, Neckeweede, or the Tristrams knot, or Saynt Andres lace, or a bastarde brothers badge, with a difference on the left side etc., you know my meaning.