A mumu.
muumuu a loose-fitting dress of Hawaiian origin, much favored by Mama Cass
It means "Hang loose". Hawaiian in origin.
The word "muumuu" is the English equivalent of the Hawaiian word muʻumuʻu , the name for a loose, hanging dress supported by the shoulders.
The Hawaiian translation of "hang loose" is "Shaka" which is commonly used as a gesture of friendship, gratitude, and solidarity.
The Hawaiian Islands are the "hang loose" chain of shield volcanoes.
A nightgown
her dress was floral print and was kind of loose fitting
enrobe
You can hire a seamstress to "take in" the seams on your dress.
They.use to be called a shift
shift
that hangs from the shoulder and is like a cross between a shirt and a robe. Like the aloha shirt, muumuu exports are often brilliantly colored with floral patterns of generic Polynesian motifs. Muumuus for local Hawaiian residents are more subdued in tone. Muumuus are no longer as widely worn at work as an aloha shirt, but continue to be the preferred formal dress for weddings and festivals such as the Merrie Monarch hula competition. Muumuus are also popular as maternity wear because they do not restrict the waist. *American is not a language; I believe the language you are referring to is English.