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1.
A french word-play on the verb go.

Derives from areas highly populated with Cajun Americans, Louisiana State University Tigers fans, or more commonly both.
"G-e-a-u-x, Geaux Tigers, Geaux!"
"Here we geaux Tigers, here we geaux!"
by Tigahfan May 07, 2004
 
2.
Cajun word...eaux makes a O sound so its GO!
Geaux Tigers(LSU).
by LSUTJM...GEAUX TIGERS January 30, 2004
 
3.
A lot of Cajun names end in -eaux (comeaux, boudreaux, thibodeaux) with an "oh" sound. So a lot of local Louisiana teams use "Geaux (insert team here)" to play off of their Louisiana and Cajun heritage. The word is often thrown around by teams but a perfect example of correct usage would be by University of Louisiana at Lafayette, Ragin Cajuns.
Geaux Cajuns!!!
by Seandroog June 06, 2010
 
4.
A sound made to distinguish an awkward or inappropriate comment/moment.

A more extreme version of "yikes".

Originates from the season 4 episode "Fast Times at Buddy Cianci Jr. High" of Family Guy.
Example 1:

Fish 1: You know what I hate? A guy in a blue suit.
Fish 2: Geaux!
Fish 3: Ssssss, there's one right behind me, isn't there?

Example 2:

Guy: I'm not sure, but I think I might be gay.
Others: Geaux!
by Ringo (stalks you) January 02, 2009
 
5.
A really stupid misspelling of "Go."
Only French idiots use "Geaux" instead of "Go."
by g0p3ns November 05, 2010