All terms in this list:

Obdurate: Unyeilding to persuasion or moral influences

Obfuscate: To render incomprehensible

Oblique: Diverging from a straight line or course, not straightforward

Obscure: Hidden by darkness; not clearly or easily seen or easily understood; relatively unknown

Obsequious: Excessively compliant or submissive

Obstreperous: Noisy, unruly

Obtuse: Lacking quickness or sensibilty or intellect

Odious: Instilling hatred or intense displeasure

Officious: Offering one's services when they are neither wanted or needed

Opulent: Characterized by rich abundance verging on ostentation