The modern spelling of the noun referring to the loose unbelted dress is muumuu, not moomoo, moo-moo, mumu, or mu-mu. The spelling is derived from the Hawaiian mu’umu’u, which in Hawaiian is properly pronounced moo-oomoo-oo. When the word entered English in the early 20th century, the apostrophes were dropped and the pronunciation simplified to moo-moo.
She may not particularly like muumuus, and she doesn’t want to be regarded as someone for whom muumuus are a reasonable choice. [New York Times]
The flowing rayon dresses lightly take inspiration from the traditional muumuu, but are transformed into contemporary looks that are fresh and sassy. [Honolulu, Waikiki, and Oahu, Sara Benson, Scott Kennedy]
Grandma Barb always wearing that massive teal muumuu — looks like a cross between Bea Arthur and Dame Edna and a giant leather ottoman. [San Francisco Chronicle]
He still performs wearing a muumuu, though. [Washington Post]