Mastery/ˈmæstəri/ Definition 1 of 2Pro Tip 1/3Specialized Knowledge Used when someone knows a lot about a particular subject or activity. She has mastery in Japanese tea ceremonies. Pro Tip 2/3Expert Level Implies reaching the highest level of skill, not just being good at something. After years of study, he achieved mastery in martial arts. Pro Tip 3/3Hard Work Highlights the effort and practice required to achieve such a high level. Her piano mastery was the result of countless hours of practice.