BIG SIOUX RIVER(noun)Did you mean?Synonyms RhymesDefinitions There is 1 meaning of the phrase Big Sioux River. Big Sioux River - as a noun A river that rises in northeastern south dakota and flows southward to join the missouri river at sioux city, iowa Word Variations & RelationsAnagramsStarts BStarts BIStarts BIGStarts BIGSEnds REnds EREnds VEREnds IVERStarts B & ends RStarts BI & ends RStarts B & ends ERA-Z Proximitiesbifurcates17bifurcating19bifurcation18bifurcations19big6 Big Sioux River big-belliedbig-bonedbig-chestedbig-shoulderedbig-ticket