Treacherous

How to spell treacherous

11 letters · 3 syllables

How to pronounce treacherous

Say the part in capitals loudest.

What does treacherous mean?

1. adjectivePresenting hidden or unpredictable dangers, especially in conditions that look safer than they are.
2. adjectiveGuilty of betraying trust or loyalty; deceitful toward those who rely on you.

Treacherous in a sentence

• The mountain path becomes treacherous after heavy rain.

• His treacherous behaviour cost him every friendship in the firm.

• Black ice made the morning commute treacherous.

• The spy was branded treacherous for selling secrets to a rival nation.

Where does treacherous come from?

Language of origin: French

This word comes from the Old French adjective trecheros or tricheros, meaning 'deceitful' or 'cheating', which was built on the verb trichier, 'to cheat or trick'. English took it on in the 1300s, first describing people who betrayed trust, exactly the way a traitor does. The same Old French verb is the ancestor of the everyday English word 'trick', so a treacherous person and a clever trick share a common root in deception. Over time the meaning widened from human betrayal to anything that secretly fails you, which is how we came to speak of treacherous ice or a treacherous road. A useful spelling note: the word is built on 'treachery', not on 'teach' or 'reach', and the soft 'ch' plus the unstressed '-erous' ending are where many adults slip.

How the word is built

• treacher- (from Old French trichier: to cheat, deceive)
• -ous (adjective suffix: full of)