The pectoralis major is the thicker, fan-shaped muscle of the human body that lies underneath the breast. It is primarily responsible for shoulder joint movement which includes (1) it enables flexion of the humerus (2) it adducts or draws the humerus towards the body (3) it rotates the humerus medially or inwards and lastly, it is responsible for the attachment of the arm to the trunk of the body.
Therefore, it is an adductor.