late Old English pil "sharp stake or stick," also, poetically, "arrow, dart," from Latin pilum, the name of the heavy javelin of the Roman foot soldier (source of Old Norse pila, Old High German pfil, German Pfeil "arrow"), a word of uncertain origin. De Vaan finds the identification of it with the pilum that means "pestle, pounder" (from *pis-tlo-, from the root of pinsere "to crush, pound;" see pestle) to be defensible.
In engineering and architecture, "a heavy timber beam, pointed or not, driven into the soil for support of a structure or as part of a wall." It also has meant "pointed head of a staff, pike, arrow, etc." (1590s) and the word is more or less confused with some of the sense under pile (n.1).
"one who or that which drives" in various senses, late 14c. (late 13c. as a surname); agent noun from drive (v.). Earliest sense is "herdsman, drover, one who drives livestock." From mid-15c. as "one who drives a vehicle." In U.S., "overseer of a gang of slaves," by 1796. Meaning "golf club for hitting great distances" is by 1892. Driver's seat is attested by 1867; figurative use by 1954.