From Middle English betrayen, bitrayen (“to commit an act of treason against”), equivalent to be- +‎ tray (“to betray”).

• IPA^(key): /bɪˈtɹeɪ/, /bəˈtɹeɪ/

• Audio (US):

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• Rhymes: -eɪ

betray (third-person singular simple present betrays, present participle betraying, simple past and past participle betrayed)

1. (transitive) To deliver into the hands of an enemy by treachery or fraud, in violation of trust; to give up treacherously or faithlessly.

   An officer betrayed the city.

2. (transitive) To prove faithless or treacherous to, as to a trust or one who trusts; to be false to; to deceive.

   to betray a person or a cause

   Quresh betrayed Sunil to marry Nuzhat.

   My eyes have been betraying me since I turned sixty.

   • c. 1590 (date written), [John Lyly], Mother Bombie. […], 2nd edition, London: […] Thomas Creede, for Cuthbert Burby, published 1598, →OCLC, Act II, scene ii:

     I maruell I heare no nevves of Dromio, either hee ſlackes the matter, or betraies his Maiſter, I dare not motion anie thing to Stellio, till I knovv vvhat my boy hath don, Ile hunt him out, if the loiterſacke be gone ſpringing into a Tauerne, Ile fetch him reeling out.

3. (transitive) To violate the confidence of, by disclosing a secret, or that which one is bound in honor not to make known.
4. (transitive) To disclose (a secret, etc.) in deliberate violation of someone’s confidence.
   • 1941, Theodore Roethke, “Feud”, in Open House, New York, N.Y.: Alfred A[braham] Knopf, →OCLC; republished in The Collected Poems of Theodore Roethke, London: Faber and Faber […], 1968, →OCLC, page 4:

     The dead leap at the throat, destroy
     The meaning of the day; dark forms
     Have scaled your walls, and spies betray
     Old secrets to amorphous swarms.

5. (transitive) To disclose or indicate, for example something which prudence would conceal; to reveal unintentionally.

   Though he had lived in England for many years, a faint accent betrayed his Swedish origin.

   • 2012 May 24, Nathan Rabin, “Film: Reviews: Men In Black 3”, in The A.V. Club‎^[1]:

     Jones’ sad eyes betray a pervasive pain his purposefully spare dialogue only hints at, while the perfectly cast [Josh] Brolin conveys hints of playfulness and warmth while staying true to the craggy stoicism at the character’s core.

   • 1966, Marc Léopold Benjamin Bloch, French rural history:

     Again, to take a less extreme example, there is no denying that although the dialects of northern France retained their fundamentally Romance character, they betray many Germanic influences in phonetics and vocabulary, […]

6. (transitive) To mislead; to expose to inconvenience not foreseen; to lead into error or sin.
7. (transitive) To lead astray; to seduce (as under promise of marriage) and then abandon.

• (to prove faithless or treacherous): sell
• (to disclose): give away

• “betray”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.
• William Dwight Whitney, Benjamin E[li] Smith, editors (1911), “betray”, in The Century Dictionary […], New York, N.Y.: The Century Co., →OCLC.

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