Armscye is a sewing term, sometimes called the Arms Eye, it simply refers to the armhole of a garment. Specifically the armscye is the fabric edge to which the sleeve is sewn.

To determine the size of the Armscye; the length of the armscye is the total length around the entire arm hole. The width of the armscye is the distance across the hole at the widest point.

Armscye is actually and accidental term that came about because of the limitations of early printing, it inadvertently became popular and stuck. However the historically correct term is "Arm's Eye"