Potassium was named after the word "potash," which means pot ashes. The K in its atomic symbol stands for its Latin name, kalium, which comes from the Arabic word "qali," which means alkali.
Before potassium was isolated as an atomic element, it was known as a component of potassium salts. Potassium carbonate, which was gathered from wood ash, was concentrated through boiling and then used for industrial purposes, such as soap making. The wood ash origin of the potassium carbonate lent the name potash to the compound (and eventually to the element).
Potassium was first isolated by Sir Humphrey Davy in 1807. He used electrolysis with a dry potash compound to identify the element. He would later use this same process to isolate sodium, which was previously undistinguished from potassium.