noun. either of two flat triangular muscles of the shoulder and upper back that are involved in moving the shoulders and arms.
1. Noun, singular or mass Full range of motion through the shoulder girdle as well as balanced strength between the upper and lower trapezius can build the foundation for a strong serve on the volleyball court so you can dominate your opponents. 2. Adjective Hold a handle in each hand and draw your shoulders up toward your ears to work your trapezius muscle, which is located in the upper and middle back region.