Wikipedia says that the word Mississippi comes from Messipi, the French rendering of the Anishinaabe (Ojibwe or Algonquin) name for the river, Misi-ziibi (Great River). This is by and large the accepted version.
I have an alternate theory. The Anishinaabe are Indo-Americans and are migrants who branched out from Dravidian tribes at some point in the misty past. Their language has many Tamil remnants and hence, it might help to analyse their place names using Tamil.
Let's take Mississippi. When examined with Tamil goggles, Mississippi feels like MUTHSIPPI or MUTHU SIPPI. Now Muthu means pearl and Sippi is Oyster. So MUTHU SIPPI just cues 'PEARL OYSTERS'.
The sceptic mind might dismiss this claim as far-fetched. But let's study the Mississippi state. One of the rivers in Mississippi is called the PEARL RIVER. And the Mississippi river has a rich history of being a lead source for pearl farming.
Given this startling coincidence, is it possible that Mississippi was MUTHU SIPPI?