-eaux

eaux is the standard French language plural form of nouns ending in eau, e.g. eau → eaux, château → châteaux, gâteau → gâteaux.

In the United States, it often occurs as the ending of Cajun surnames, as well as a replacement for the long "O" sound in some English words as a marker of Cajun, or more broadly Louisiana, identity.

American surnames
eaux, pronounced with a long "O" sound, is a common ending in the United States for historically Cajun surnames, such as Arceneaux, Boudreaux, Breaux, Robicheaux, and Thibodeaux. The same surnames in Quebec and elsewhere in Canada are generally spelled without a terminal x. However, several common Cajun surnames, especially ones that start with a "C", retain the eau ending, for example, Cousineau.

Although there is debate about the exact emergence of the eaux 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. Because many Cajun surnames 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 sound. Brasseaux credits St. Martin Parish Judge Pierre Paul Briant for standardizing the "eaux" spelling of these names during his oversight of the 1820 U.S. Census. In addition, the counts of Pontchartrain and Maurepas spelled their surname 'Phélypeaux', among others, indicating a precedence for the "x" spelling in at least some parts of France.

English-language use in Louisiana
The use of eaux as a replacement for in English-language contexts can be considered a salient feature of English usage in Louisiana. It is used in Louisiana as a marker of Cajun (or more broadly Louisiana) heritage, particularly at collegiate and professional sporting events, typified as "Geaux Tigers", "Geaux Cajuns", or "Geaux Saints" being pronounced as "Go Tigers", "Go Cajuns", and "Go Saints". Louisiana State University trademarked the phrase "Geaux Tigers" in 2005, and University of Louisiana at Lafayette similarly trademarked "Geaux Cajuns" in 2014.

However, in the French language, a letter "e" or "i" that immediately follows a "g" will cause the "g" to become soft. Therefore the pronunciation of "geaux" is actually, and not. Preserving the hard g-sound would either require removing the "e" (resulting in gaux) or inserting a silent "u" after "g" (gueaux).