When the word cash was first attested in English in 1595, it referred to a box where you store your money, and it wasn't until 1677 that it was used to mean "money" in general. The word comes from French caissa, which was taken in the early sixteenth century from Latin capsa, meaning "box". Capsa, which is also the source of the words chassis, case, and capsule, comes from the verb capere, meaning "to seize" (and capere is also the etymon of a bunch of words, including incipient, capture, capiche, forceps, deceive, and dozens more). Finally, that derives from the Proto-Indo-European reconstruction kehp, meaning "grasp". Cash was first used as a verb in 1811 (encash was briefly a thing in the 1860s, but that died out), which helped account for an increase in usage in the nineteenth century.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.