Humphry Davy’s name for potassium is from “potash,”
which is from the fact that it was obtained from leaf or wood ashes in a pot.
It might seem arbitrary; however, the origin of kalium in Latin is similar.
Kalium is from Arabic al qalīy,
which means “plant ashes.” The origin of language
is association, or, as Ezra Pound claimed, all language is buried metaphor.
See also in The book of science:
Readings on wikipedia: