Definition of "hurdle"

My last stop was an outdoor speech to a huge crowd of Ukrainians whom I urged to stay on the course of freedom and economic reform. Kiev was beautiful in the late spring sunshine, and I hoped its people could keep up the high spirits I had observed in the crowd. They still had many hurdles to clear.

2005, Bill Clinton, My Life‎, volume II, New York: Vintage Books, page 588

The practice of folding sheep was general, and the purchase of hurdles was a regular charge in the shepherd's account.

1882, James Edwin Thorold Rogers, A History of Agriculture and Prices in England, volume 4, page 414

In treason, the corporal punishment is by drawing on hurdle from the place of the prison to the place of execution, and by hanging and being cut down alive, bowelling, and quartering: and in women by burning.

1550, Francis Bacon, “A Preparation Toward the Union of Laws”, in James Spedding, Robert Leslie Ellis, Douglas Denon Heath, editors, The Works of Francis Bacon‎, volume VII, London: Longman, Green & Co., page 735

Such a crew! Ah! many a wretch has rid on hurdles who has done less mischief than these utterers of forged Tales, coiners of Scandal, and clippers of Reputation.

1777, Richard Brinsley Sheridan, The School for Scandal, II.i

Hurdles, with four, five, six wretches convicted of counterfeiting or mutilating the money of the realm, were dragged month after month up Holborn Hill. On one morning seven men were hanged and a woman burned for clipping

1851, Thomas Babington Macaulay, chapter 21, in The History of England from the Accession of James the Second, volume IV, London: Longman, Brown, Green, and Longmans

Behind flock'd wrangling up a piteous crew, / Greeted of none, disfeatur'd and forlorn— / Cowards, who were in sloughs interr'd alive: / And round them still the wattled hurdles hung / Wherewith they stamp'd them down, and trod them deep, / To hide their shameful memory from men.

1855, Matthew Arnold, Balder Dead, Part II, in The Poems of Matthew Arnold, 1840-1867, Oxford University Press, 1909, pp. 250-51

Watching where shepherds pen their flocks at eve In hurdled cotes amid the field secure

1667, John Milton, “(please specify the book number)”, in Paradise Lost. […], London: […] [Samuel Simmons], […]; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873,