"to make into scrap, consign to a scrap-heap, break up (machinery) into scrap-iron," 1883 (in reference to locomotives), from scrap (n.1). Related: Scrapped; scrapping; scrappable.
1510s, "to enclose with a fence;" c. 1600 as "to enclose or fortify with an embankment;" see mound (n.). From 1859 as "to heap up." Related: Mounded; mounding.
Meaning extended by early confusion with obsolete bouk "belly" (from Old English buc "body, belly," from Proto-Germanic *bukaz; see bucket), which led to sense of "size, volume, magnitude of material substance," attested from mid-15c. In bulk 1670s, "loaded loose." Meaning "the greater part" (of anything) is by 1711.
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.