Preposterous (adjective)

1. Completely unreasonable and ridiculous.
2. Completely contrary to nature, reason, or common sense.

Origin:

Early 17th century: from latin praeposterus "backwards" (from prae "before" + posterus "following") + -ous.

Examples:

1. It's preposterous to suggest that the company is responsible.
2. It's preposterous to think that they would agree to such a proposal.
3. The idea was preposterous.
4. A preposterous claim.
5. A preposterous situation.