Absurd (adjective)

1. Wildly unreasonable, illogical, or inappropriate.
2. So obviously false or ridiculous as to be laughable.

Origin:

Early 17th century: from latin absurdus "out of tune", from ab- "away from" + surdus "deaf".

Examples:

1. The idea that aliens built the pyramids is absurd.
2. It is absurd to think that a small company can compete with a giant corporation.
3. The accusations are absurd and without any evidence.
4. The argument is absurd, as it is based on a false premise.
5. The notion that the earth is flat is an absurd belief.