Improbable

Part of speech: adjective

Pronunciation: /ɪmˈpɹɑbəbl̩/

Definitions

1. Not likely to occur or be factual based on evidence or expectation
2. Having a very low chance of happening or being accurate in reality
3. Describing something that is doubtful to take place or be correct given the circumstances

Etymology: Latin "probabilis" meant "credible" or "worthy of approval," and it came from "probare," "to test" or "to prove." So "probable" once carried a sense of being provable or deserving trust, and only later drifted toward "likely." "Improbable" is formed by adding the negating prefix "im-" to that root, giving the sense of something not worthy of belief or not supported by evidence. English took the word directly from Latin "improbabilis," with the "im-" prefix matching the Latin negating prefix. Its basic meaning is still that of something that is unlikely to happen, the opposite of the modern "probable."

Synonyms: unlikely, dubious, questionable

Antonyms: probable, likely, certain