Frock

In Australia it is frequently used this way, with the phrase "to frock up" meaning to wear a formal dress or gown for a special occasion.

Originally, a frock was a loose, long garment with wide, full sleeves, such as the habit of a monk or priest, commonly belted.

Throughout the early modern period, "frock" continually applied to various types of clothing, but generally denoting a loosely fitted garment in practice seemingly ranging in styles from resembling a banyan to a tunic.

From the 17th century on, a frock was a thigh- or full-length loose outer garment worn by shepherds, workmen, and farm workers in Great Britain, generally of heavy linen with a broad flat collar, now usually called a smock-frock.

In contemporary times, a "frock" may still designate a woman's or girl's, or child's dress or light overdress.

Charles Blair in a frock (c. 1761–66), a coat with a flat collar.
Johann Reinhold Forster with his son Georg Forster (1780) in frocks in Tahiti , by John Francis Rigaud (1742–1810).
Man's wool and silk twill frock coat , France (1816–20), illustrating the shift from previous 18th century connotations of a frock to early 19th century definition of a (dark) frock coat. Los Angeles County Museum of Art .
The "frock" as a dress, worn by a woman.