Pison

"Babylonian, the current, broad-flowing, one of the "four heads" into which the river which watered the garden of Eden was "divided (Gen. 2:11). Some identify it with the modern Phasis," "others with the Halys, others the Jorak or Acampis, others the" "Jaab, the Indus, the Ganges, etc."

Definition of Pison:
"changing; extension of the mouth"