A professional who makes women's clothing, especially Western-style dresses. The term implies a skilled craftsperson, often working in a tailor shop or independently.
She has worked as a dressmaker for many years.
I had a dressmaker make a dress for me.
A designer, often focusing on creative design rather than the actual sewing. 洋裁師 is more hands-on with garment construction.
Compound of 洋裁 (Western-style sewing/dressmaking) and 師 (master, expert). The term is transparently derived from its components.