pectoralis

/ˌpɛktəˈrælɪs/
noun
  1. Either of two large chest muscles (pectoralis major and pectoralis minor) that move the shoulder and arm.
    • Swimmers often develop strong pectoralis muscles from repetitive arm strokes.
    • The anatomy diagram labels the pectoralis major as the large fan-shaped muscle in the upper chest.
    • He strained his pectoralis while lifting weights at the gym.