[ trech-er-uhs ]
/ ˈtrɛtʃ ər əs /


characterized by faithlessness or readiness to betray trust; traitorous.
deceptive, untrustworthy, or unreliable.
unstable or insecure, as footing.
dangerous; hazardous: a treacherous climb.

Nearby words

  1. trayf,
  2. traymobile,
  3. trazodone,
  4. trc,
  5. tre corde,
  6. treacherously,
  7. treachery,
  8. treacle,
  9. treacle mustard,
  10. tread

Origin of treacherous

1300–50; Middle English trecherous < Anglo-French, equivalent to trecher deceiver (trech(ier) to deceive + -er -er2) + -ous -ous. Cf. French tricheur trickster

Related forms Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for treacherous

British Dictionary definitions for treacherous


/ (ˈtrɛtʃərəs) /


betraying or likely to betray faith or confidence
unstable, unreliable, or dangeroustreacherous weather; treacherous ground
Derived Formstreacherously, adverbtreacherousness, noun

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for treacherous



early 14c., from Old French trecheros (12c.), from trecheur, agent noun from trechier "to cheat, trick" (see trick). Figuratively, of things, from c.1600. Related: Treacherously; treacherousness.

Online Etymology Dictionary, © 2010 Douglas Harper