Fallacious

Part of speech: adjective

Pronunciation: /fəˈleɪ.ʃəs/

Definitions

1. Containing or resulting from a mistaken belief or faulty logic
2. Relying on unsound arguments or deceptive reasoning
3. Involving errors in reasoning that lead to false or misleading conclusions

Etymology: Fallacious traces back to Latin "fallere," meaning "to deceive" or "to trip up," the same root that gives English "fail" and "false" through other routes. Its Latin relative "fallax" described something that deceives, and "fallacia" was the noun for a trick or deception. The idea is literal at heart: a deceptive thing is one that makes you stumble. The word passed into English through Old French "fallacieux," which added the adjective ending "-ieux" to the Latin base. English speakers then fitted the ending into the form we use today, "-acious," so the adjective sounds like a close cousin of words such as "audacious" and "tenacious." Its sense was "deceptive" or "given to deceit" long before it narrowed to describing faulty reasoning.

Synonyms: misleading, deceptive, erroneous, false, spurious

Antonyms: truthful, accurate, valid