-eaux is the standard French language plural form of nouns ending in -eau, e.g. eau → eaux, château → châteaux, gateau → gateaux.
In the USA, it often occurs as the ending of Cajun surnames.
This is a common ending in the United States for historically Cajun surnames, such as Arceneaux, Babineaux, Boudreaux, Breaux, Legeaux, Marceaux, Robicheaux, Seaux and Thibodeaux. This combination of letters is pronounced with a long "O" sound /oʊ/.
United States spelling and use
Although there is debate about the exact emergence of this spelling in the United States, it has been claimed that the spelling originated from immigrants who did not speak or read English having to make an "x" mark at the end of their printed name in order to sign a legal document. Since many Cajun names of French origin already ended in "-eau," the names' endings eventually became standardized as "-eaux."
This claim has been disputed by the historian Carl Brasseaux, who insists that the "-eaux" ending was one of many possible ways to standardize Cajun surnames ending in an "O" sound. Brasseaux claims that Judge Paul Briant is most responsible for the "-eaux" ending during his oversight of the 1820 U.S. Census in Louisiana and that the "x" ending is completely arbitrary. In addition, the counts of Pontchartrain and Maurepas spelled their surname "Phelypeaux", indicating that at least some literate settlers of Louisiana used that ending.
Several surnames end in -eau (the standard French spelling), especially surnames that start with "C", as in Cousineau, a common Cajun surname.
The "-eaux" ending is used among residents of south Louisiana as a marker of their Cajun heritage, particularly at sporting events for Louisiana State University, McNeese State University, Nicholls State University, and the University of Louisiana at Lafayette on signs like "Geaux Tigers," "Geaux Cowboys," "Geaux Colonels," "Geaux Saints," or "Geaux Cajuns.", being pronounced as "Go Tigers," "Go Cowboys," "Go Colonels," "Go Saints," or "Go Cajuns".
Steve-O's line of shoes, labeled "Sneaux Shoes", are also pronounced /ˈsnoʊʃuːz/ (snow shoes).