c. 1300, "to strip (someone) of clothes, strip a slain enemy," from Old French espillier "to strip, plunder, pillage," from Latin spoliare "to strip, uncover, lay bare; strip of clothing, rob, plunder, pillage," from spolia, plural of spolium "arms taken from an enemy, booty;" originally "hide, skin stripped from a killed animal," from Proto-Italic *spolio- "skin, hide," from PIE *spol-yo-, probably from a root *spel- "to split, to break off" (see spill (v.)) on the notion of "what is split off."
From late 14c. in English as "strip with violence, rob, pillage, plunder, dispossess; impoverish with excessive taxation." Used c. 1400 as the verb to describe Christ's harrowing of Hell. Sense of "destroy, ruin, damage so as to render useless" is from 1560s; that of "to over-indulge" (a child, etc.) is from 1640s (implied in spoiled). Intransitive sense of "become tainted, go bad, lose freshness" is from 1690s. To be spoiling for (a fight, etc.) is from 1865, from notion that one will "spoil" if he doesn't get it.