"mass, heap," early 15c., originally "pillar, pier of a bridge," from Middle French pile and directly from Latin pila "stone barrier, pillar, pier" (see pillar). Sense development in Latin from "pier, harbor wall of stones," to "something heaped up." In English, sense of "heap of things" is attested from mid-15c. (the verb in this sense is recorded from mid-14c.). The meaning "large building" (late 14c.) is probably the same word.