late 14c., "act of plundering" (especially in war), from Old French pilage (14c.) "plunder," from pillier "to plunder, loot, ill-treat," possibly from Vulgar Latin *piliare "to plunder," probably from a figurative use of Latin pilare "to strip of hair," perhaps also meaning "to skin" (compare figurative extension of verbs pluck, fleece), from pilus "a hair" (see pile (n.3)).
Pillage and spoil especially suggest the great loss to the owner, completely stripping or despoiling them of their property ; plunder suggests the quantity and value of that which is taken : as, loaded with plunder; booty is primarily the spoils of war, but also of a raid or combined action, as of pirates, brigands, or burglars .... [Century Dictionary]
"to plunder, despoil, strip of money or goods by open violence," 1590s, from pillage (n.). Related: Pillaged; pillaging; pillager. The earlier form of the verb in English was simply pill (late Old English pilian), which probably is from Medieval Latin pillare.