It comes from potash. This word comes from the ashes of a wood fire, on which your pot was boiling.
Potassium is a generic name. The chemical substance is potassium.
The compound name of potassium and iodine is potassium iodide.
Potassium thiocyanate is the name for KSCN.
The compound name of potassium and bromine is potassium bromide.
potassium nitrite
The compound name for KCl is potassium chloride.
Another name for potassium hydrogen carbonate is potassium bicarbonate.
The name of the ionic compound K2SO4 is potassium sulfate.
The compound name for K3PO2 is potassium hypophosphite.
The elements in the compound potassium oxide are potassium and oxygen.
The name aluminium is derived from the antic name of potassium aluminium sulfate - K2Al6(OH)12(SO4)4 - alumen.
There really aren't any, since potassium is not something you find lying around (it's way too reactive). Potassium hydroxide has a common name of "lye" if that helps. You might also hear it called "potash" (which is where the word potassium comes from).