[ gdw]
This term has two possible Latin etyma, both of which could have generated these forms and this meaning. On the one hand, both palus, related to pal1(‘stake, fence’) and medieval Latin pelum (‘stake, fence’, ultimately also from palus but influenced by vernacular pel) refer to a round fortress within a palisade; on the other, pila, related to pile3 (‘pillar, pile’), refers to a fortified tower.