Ridiculous (adjective)

1. Deserving or inviting derision; absurd.
2. Extremely or utterly absurd or unreasonable.

Origin:

Late 16th century: from latin ridiculus "laughable", from ridere "to laugh".

Examples:

1. The idea that aliens built the pyramids is ridiculous.
2. It's ridiculous to think that you can run a marathon without training.
3. The amount of money they are asking for is ridiculous.
4. The story was so ridiculous that no one believed it.
5. The way he was dressed was ridiculous.