BIG SIOUX RIVER(noun) Did you mean: Synonyms Rhymes Definitions 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 & RelationsAnagrams Starts B Starts BI Starts BIG Starts BIGS Ends R Ends ER Ends VER Ends IVER Starts B & ends R Starts BI & ends R Starts B & ends ER A-Z Proximitiesbifurcates 17bifurcating 19bifurcation 18bifurcations 19big 6 Big Sioux River big-belliedbig-bonedbig-chestedbig-shoulderedbig-ticket