1. the quality or state of being relaxed, informal, or unconcerned
2. lack of careful attention or thoroughness

Examples

• The casualness of his dress surprised everyone at the formal dinner.
• She spoke with a casualness that masked her nervousness.
• The casualness of their approach to the project led to several mistakes.
• His casualness about the deadline worried his supervisor.
• The restaurant’s casualness made it perfect for a relaxed family meal.
• The casualness with which he handled the expensive equipment made me nervous.