early 15c., "heap or stack of something," usually consisting of an indefinite number of separate objects arranged in a more or less regular conical or pyramidal form, from Old French pile "a heap, a stack," and directly from Latin pila "a pillar," also "stone barrier, pier" (see pillar).
The sense development in Latin would have been from "pier, harbor wall of stones," to "something heaped up." Middle English pile also could mean "pillar supporting something, pier of a bridge" (mid-15c.). In English, the verb in the sense of "to heap (up)" is recorded from c.1400.
Middle English also had a noun pile meaning "castle, tower, stronghold (late 14c.), which persisted in a sense of "large building." OED regards this as a separate word, of doubtful origin, but other sources treat them as the same.
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).
mid-14c., "downy plumage;" late 15c, "fine, soft hair," from Anglo-French pyle or Middle Dutch pijl, both from Latin pilus "a hair" (source of Italian pelo, Old French pel), a word of uncertain origin. Phonological evidence rules out transmission of the English word via Old French cognate peil, poil. Meaning "soft, raised surface of a regular and closely set kind upon cloth" is from 1560s.
"to heap (up), lay or throw in a heap," c. 1400, from pile (n.1). Related: Piled; piling. Figurative verbal phrase pile on "attack vigorously, attack en masse," is attested by 1894, American English. To pile in "climb or go on or into in a crowd" is by 1841; hence, for the reverse process, pile out, by 1896.