The word pillar is from the French word pilier, which is from Latin word pilare, which in turn is from the earlier Latin word pila. All of these words meant the exact same thing, and they continue to mean the exact same thing as we go back to Proto-Italic pistla and Proto-Indo-European pistlo, Needless to say, pillars have been around a long time, with little need for variation, semantically or in spelling. This changes as we go back to the even earlier PIE root peys, which meant "to crush"; a pillar is stone, and stones are crushed. Now, peys is also the root of several other words. Also through the pistlo route, it's the root of the word pilum (a type of Roman spear that "crushes" its enemies, I suppose), and it lead to the Latin verb pinsere, or "to pound", which later gave way to pestone, a word that meant "pestle" (a tool for grinding stuff; here the connections are clearest), and through both Italian and French, it was altered in phonetics and definition to become piston, an Italian invention. All these things that needed to be created came from naught but crushings. How scintillating!
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.