Which term describes an overbearing or fearless attitude?

The term that best describes an overbearing or fearless attitude is "imperious." This word conveys a sense of domination, authority, and a commanding presence that often comes across as arrogant or overbearing. People who are described as imperious tend to demand obedience or attention from others, reflecting a strong, sometimes excessive confidence in their own capabilities or status.

In contrast, while "hubris" can also refer to excessive pride or self-confidence often leading to downfall, it doesn't necessarily capture the commanding or authoritative nature implied by imperiousness. "Idyll" refers to a happy, peaceful, or picturesque scene or experience, which is unrelated to attitude. "Hirsute" describes something related to hairiness or having hair, and does not pertain to attitude at all. Thus, "imperious" is the most fitting term for describing an overbearing demeanor.