The incorrectly spelled word is:

 Conscientous

The correct spelling is "Conscientious." Conscientious means to be diligent, careful, and thorough in one's work or duties.

The other options are spelled correctly:

• Inscrutable: Describes something that is difficult to understand or interpret.
• Banality: Refers to something that is ordinary, common, or lacking originality.
• Giddyap: This is a colloquial term for urging or encouraging a horse to go faster, typically used in horse riding or driving.