1. difficult in a way that tests one’s abilities or resources
2. stimulating and rewarding despite being difficult
3. questioning or disputing something in a confrontational way

Examples

• The math test was very challenging for most students.
• She found rock climbing to be a challenging but enjoyable hobby.
• The new job offers challenging opportunities for growth.
• His challenging attitude made the meeting uncomfortable.
• The challenging terrain required special equipment.
• The professor gave us a challenging assignment over the weekend.
• She gave him a challenging look when he disagreed.