spoil: [13] Latin spolium originally denoted ‘skin stripped from a killed animal’ (it went back ultimately to the Indo-European base *spel- ‘split, burst’, which also produced German spalten ‘split’, and probably English spill and split). It broadened out metaphorically via ‘weapons stripped from a fallen enemy’ to ‘booty’ in general, which lies behind English spoils.
The word itself was borrowed from Old French espoille, a derivative of the verb espoillier, which in turn went back to Latin spoliāre ‘despoil’ (source of English spoliation [14]), a derivative of spolium. The verb spoil came either from Old French espoillier, or is short for despoil [13], which went back via Old French despoillier to Latin dēspoliāre.
It used to mean ‘strip of possessions’, as despoil still does, but in the 16th century it moved across to take over the semantic territory of the similarsounding spill (which once meant ‘destroy, ruin’). => despoil, spoliation
spoil (v.)
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 "skin stripped from a killed animal," from PIE *spol-yo-, perhaps from root *spel- "to split, to break off" (see spill (v.)).
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.
spoil (n.)
"booty, goods captured in time of war," mid-14c., spoils (collective singular), from spoil (v.) or else from Old French espoille "booty, spoil," from the verb in French, and in part from Latin spolium. Also from the Latin noun are Spanish espolio, Italian spoglio.
Transferred sense of "that which has been acquired by special effort" is from 1750. Spoils has stood cynically for "public offices, etc." aince at least 1770. Spoils system in U.S. politics attested by 1839, commonly associated with the administration of President Andrew Jackson, on the notion of "to the victor belongs the spoils."