What is an armscye?
An armscye is a tailoring term that stands for the measurement of arm hole in a bodice, doublet, etc. It is the big gap provided at the beginning of your shoulder for your arm to pass through.
To measure armscye for your dress you should ideally begin from the tip of the shoulder, go around the arm and come back to the tip. To be more accurate you should feel for the bone’s end in your shoulder, and it should serve as the starting point for the measurement.