The option that can be used as a one-word substitute for the given group of words "Having or showing an excessively high opinion of one's appearance, abilities, or worth" is "Vain."

Explanation of the options:

☀ Superior: This word refers to someone or something of higher rank, quality, or importance.

☀ Vain: This word describes someone who is excessively proud or concerned with their own appearance, abilities, or achievements.

☀ Otiose: This word means serving no practical purpose or being ineffective or futile.

☀ Domineering: This word describes someone who exercises control or influence over others in an authoritarian or overbearing manner.