Betray
Middle English: from be- ‘thoroughly’ + obsolete tray ‘betray’, from Old French trair, based on Latin tradere ‘hand over’.
wiktionary
From Middle English betrayen, betraien, equivalent to be- + tray(“to betray”). English tray(“to betray”) derives from Middle English traien, from Old French traïr(“to commit treason, betray”), from Latin trādō(“to deliver, give over”). Compare also traitor, treason, tradition. In English betrayen meant solely “to commit an act of treason against someone; deliver someone treasonably to an enemy; betray one's trust; deceive, mislead”. The modern sense “to disclose, discover, reveal unintentionally” is due to influence from or merger with English bewray(“to reveal, divulge”), which is similar in sound and meaning. The similarity with German betrügen, Dutch bedriegen, from Proto-West Germanic *bidreugan(“to betray, deceive”), is coincidental.
etymonline
betray (v.)
early 13c., "prove false, violate by unfaithfulness;" c. 1300, bitrayen, "deliver or expose to the power of an enemy by treachery," also "mislead, deceive, delude," from be- + obsolete Middle English tray, from Old French traine "betrayal, deception, deceit," from trair (Modern French trahir) "betray, deceive," from Latin tradere "hand over," from trans "across" (see trans-) + dare "to give" (from PIE root *do- "to give").
From 1580s as "unintentionally show a true character;" 1690s as "indicate what is not obvious." From 1735 as "reveal or disclose in violation of confidence." Sometimes in Middle English also bitraish, betrash, from the French present participle stem. Related: Betrayed; betraying.
