Merriam-Webster's Advanced Learner's Dictionary:
gymnastics
gym·nas·tics /ʤɪmˈnæstɪks/ noun
1 [noncount]
a : physical exercises for developing strength and balance
• They limbered up by practicing some gymnastics on the mat.
b : a sport in which athletes are judged on how well they perform various physical exercises on a mat or on special equipment
• She won an Olympic gold medal in gymnastics.
• He teaches gymnastics at the local high school.
2 [plural] : an activity that requires unusual ability or effort
• The singer's vocal gymnastics are impressive.
• It makes sense, but only after some complicated mental gymnastics.
- gym·nas·tic /ʤɪmˈnæstɪk/ adj
• gymnastic moves
• a gymnastic exhibition