• IPA: /ɹeɪn/

From Middle English rein, reyne, borrowed from Anglo-Norman resne, from la-eme retina, ultimately from Classical Latin retineō, from re- + teneō.

Displaced native Old English ġewealdleþer (literally “control leather”).

rein (plural reins)

1. A strap or rope attached to a bridle or bit, used to control a horse, animal or young child.
2. (figurative) An instrument or means of curbing, restraining, or governing.

   The government is attempting to keep a rein on rising prices.

   • 1667, John Milton, “Book X”, in Paradise Lost. […], London: […] [Samuel Simmons], and are to be sold by Peter Parker […]; [a]nd by Robert Boulter […]; [a]nd Matthias Walker, […], →OCLC ↗; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873, →OCLC ↗:

     Let their eyes rove without rein.

• French: rêne
• German: Zügel
• Italian: redine, briglia
• Portuguese: rédea
• Russian: по́вод
• Spanish: rienda

rein (reins, present participle reining; simple past and past participle reined)

1. (transitive) To direct or stop a horse by using reins.
   • [1611?], Homer, “(please specify |book=I to XXIV)”, in Geo[rge] Chapman, transl., The Iliads of Homer Prince of Poets. […], London: […] Nathaniell Butter, →OCLC ↗; republished as The Iliads of Homer, Prince of Poets, […], new edition, volume (please specify the book number), London: Charles Knight and Co., […], 1843, →OCLC ↗:

     He mounts and reins his horse.

     The spelling has been modernized.

2. (transitive) To restrain; to control; to check.
   • c. 1608–1609 (date written), William Shakespeare, “The Tragedy of Coriolanus”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC ↗, [Act III, scene iii]:

     Being once chafed, he cannot / Be reined again to temperance.

   • 2001, Jonathan Franzen, The Corrections:

     After an interval that he judged to have lasted twenty minutes, the bed began to shake with poorly reined sobs.

3. (intransitive) To obey directions given with the reins.
   • 2011, Marie Claire Peck, Rocking Horse Ranch, page 40:

     She worked each horse at a walk, trot, and then a canter. The horses reined well and executed stops quickly.

From Anglo-Norman - reines, Middle French reins, and their source, Latin rēnēs.

rein (plural reins)

1. (now rare, archaic, chiefly in plural) A kidney.
   • 1603, Michel de Montaigne, chapter 12, in John Florio, transl., The Essayes […], book II, London: […] Val[entine] Simmes for Edward Blount […], →OCLC ↗:

     a man subject to these like imaginations […] hath often the stone imaginarily, before he have it in his reines […].

   • 1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], →OCLC ↗, Lamentations 3:13 ↗:

     He hath caused the arrows of his quiver to enter into my reins.

2. The inward impulses; the affections and passions, formerly supposed to be located in the area of the kidneys.
   • 1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], →OCLC ↗, Proverbs 23:16 ↗:

     My reins rejoice, when thy lips speak right things.

   • 1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], →OCLC ↗, Revelation 2:23 ↗:

     I am he which searcheth the reins and hearts.

• As a German surname, borrowed from German Rein, comparable to the first element of several surnames such as Reinhardt, Reinbold, etc.
• As an English surname, variant of Rain. Possibly also a habitational surname related to Rhine.

1. Surname.

rein (uncountable)

1. (telecommunication) Acronym of repetitive electrical impulse noise

   Coordinate term: SHINE