free rein

dated plural free reins · alternative free reign

1. equestrianismA rein of a horse held loosely so that the animal can move more freely; also, the free condition that this gives to a horse.

   So ceased the sea's uproar, when its grave Sire / Looked o'er th' expanse, and, riding on in light, / Flung free rein to his winged obedient car.

   1908, Virgil, “Book I”, in Theodore C[hickering] Williams, transl., The Æneid of Virgil Translated into English Verse, Boston, Mass.; New York, N.Y.: Houghton Mifflin Company […], published [1910], →OCLC, page 8

   2 more examples

   I needed no whip, or spur, for I was as eager as my rider: he saw it, and giving me a free rein, and leaning a little forward, we dashed after them.

   [1877], Anna Sewell, “The Lady Anne, or a Runaway Horse”, in Black Beauty: […], London: Jarrold and Sons, […], →OCLC, part II, page 113

   [I]n the rise during the leap, just previous to the spring, no efforts whatever must be made by the rider to support the horse, or to lift him, but instead, she should simply hold the reins so lightly that his mouth can just be felt, which is called "giving a free rein."

   1884, Elizabeth [Platt] Karr, “The Leap—the Standing Leap—the Flying Leap”, in The American Horsewoman, Boston, Mass.; New York, N.Y.: Houghton, Mifflin and Company […], →OCLC, page 256

2. figurativelyThe absence of constraints; freedom to act, decide, or speak.

   to give [a] free rein to

   5 more examples

   [H]e vvas pleas'd to lend / Free reines to mirth, and to ſuſpend thoſe cares / That claime ſuch intereſt in th' Imperiall brovv.

   a. 1645 (date written), Fra[ncis] Quarles, The Virgin Widow. A Comedie, London: […] R[ichard] Royston, […], published 1649, →OCLC, Act I, page 1

   [Geoffrey] Chaucer gave a free rein to his poetical mirth.

   1790, Thomas Pennant, “[Chaucer]”, in Of London, London: […] Rob[er]t Faulder, […], →OCLC, page 47

   If you have any influence, therefore, on members of Congress, on editors, on the creators of public opinion, on your neighbors, on the rank and file of your army, teach them that with Massachusetts bayonets, it is better to be insubordinate, and shoot a Colonel, than it is, unasked, unauthorized, and Heaven-damned, to turn themselves into hunters of slaves. (Loud and prolonged cheers.) Help the Government to dare to give free rein to the ardor of the people.

   1861 August 9, Wendell Phillips, “Speech of Wendell Phillips, Esq. at the celebration of W. I. emancipation”, in W[illia]m Lloyd Garrison, editor, The Liberator, volume XXXI, number 32 (number 1598 overall), Boston, Mass.: J[ames] B[rown] Yerrinton & Son, […], →ISSN, →OCLC, page 1, column 6

   At the suggestion of the latter [Bardas], Michael [III] sought the assistance of Ignatius [of Constantinople] in an effort to force Theodora to enter a convent, in the hope of securing for himself an undivided authority and a free rein for his profligacy. The patriarch indignantly refused to be a party to such an outrage. Theodora, however, realizing the determination of her son to possess at any cost an undivided rule, voluntarily abdicated.

   1913, John B. O’Connor, “Ignatius of Constantinople, Saint”, in Charles G[eorge] Herbermann, Edward A[loysius] Pace, Condé B[enoist] Pallen, Thomas J[oseph] Shahan, John J[oseph] Wynne, editors, The Catholic Encyclopedia: An International Work of Reference on the Constitution, Doctrine, Discipline, and History of the Catholic Church […], special edition, volume VII, New York, N.Y.: The Encyclopedia Press, →OCLC, page 647

   Such hedging is necessitated by the lack of in-depth knowledge of the contents, which also gives free rein to the scripting of unsubstantiated factoids concerning the book.

   2018 December, James Lambert, “Setting the Record Straight: An In-depth Examination of Hobson-Jobson”, in Robert Lew, editor, International Journal of Lexicography, volume 31, number 4, Oxford, Oxfordshire: Oxford University Press, →DOI, →ISSN, →OCLC, page 487

   Synonyms: blank check, blank cheque, carte blanche, free hand, proxy in blank