Originally, a frock was a loose, long garment with wide, full sleeves, such as the habit of a monk or priest, commonly belted. ... In some areas, this traditional frock buttons up the front in the manner of a coat, while in others it is a pullover style.

Use the noun frock as an old-fashioned way to say "dress." You might wear a new pink frock to your best friend's birthday party. Typically, girls and women wear frocks, especially to formal events like weddings and fancy parties. ... You can also call a monk's loose, long-sleeved garment a frock.