A word for several kinds of wreckage
English now uses spoiler for more than one kind of damage. The sense most people meet first is a plot leak: a review, a comment, or a thumbnail that hands over a death, a twist, or an ending before the reader has lived through the story. The same noun still names a candidate who cannot win but can drain votes from someone who might, a fighter whose only real talent is to wreck another boxer's rhythm, and the hinged plate on a wing or a car that dumps lift on purpose. Those jobs look unrelated until they are lined up. Each one names a person or a device that takes away what someone else hoped to keep: surprise, victory, or airflow.
Tracking the origin of the word spoiler means starting not with forums but with plunder. The noun is an ordinary English agent form, spoil plus the suffix -er. The verb behind it arrived from French and Latin with a much bloodier task than ruining a season finale.
How spoil reached English
The verb is a borrowing, not a native Germanic inheritance. Around 1300, Middle English has spoilen, taken from Anglo-French espoiller and Old French espoillier, and also from Latin spoliare, to strip, uncover, rob, or pillage. The Oxford English Dictionary's earliest evidence for the English verb falls in the Middle English period, around 1330. American Heritage traces the same path: Middle English spoilen, from Old French espoillier, from Latin spoliare, from spolium, booty.
That Latin noun is the older picture. Spolium first named the hide stripped from a killed animal. It then named the arms taken off a fallen enemy, and from there the general loot of war, often in the plural spolia. The English noun spoil, frequently spoils, is recorded from about 1300 in that military sense: goods seized in conflict, and also the act of ravaging. Spanish espolio, Italian spoglio, and Welsh ysbail sit on the same Latin noun. English despoil, from Old French despoillier, is a close cousin rather than a child of spoil itself.
Historical linguists usually reconstruct Latin spolium from a Proto-Italic form for skin or hide, and behind that a Proto-Indo-European root *spel- meaning to split or break off: the hide as what is split from the body. Proposed relatives include Greek words for hide, Old High German spaltan to split, Lithuanian spaliai for flax shives, and Sanskrit sphatayati, splits. That deeper root is a reconstruction, not a chain of dated texts, and it should be treated as probable rather than proven. What the written languages do show is the move from stripped skin to stripped armor to booty.
Building the agent noun
Once spoil was in English, -er did the usual work of naming the person who performs the action. Dictionaries agree on the morphology and on the first sense, a plunderer or pillager, but they do not agree on the first year. One standard etymology dictionary places spoiler around 1400. Merriam-Webster is content with the fifteenth century. The Oxford English Dictionary dates the noun to 1535. Those are different earliest citations, not rival theories of where the word came from. The stable fact is the meaning: a robber, a despoiler, someone who strips.
The verb did not stay in the camp of war. By the late fourteenth century it could mean to strip a place by force, to dispossess, or to take an essential quality away. From the 1560s it could mean to ruin something so that it was no longer useful. The 1640s give the overindulged child; the 1690s give food going bad. After about 1600 the old sense of stripping the dead faded. By the time Modern English used spoil for milk or for a child's manners, the agent noun was ready to follow the verb into new work. The morphology never changed. Only the thing being spoiled did.
Lift, contests, and plots
Aviation took the word in the late 1920s. A spoiler on a wing is a plate that rises into the airflow and wrecks the smooth stream that produces lift. The name is literal: the device spoils lift. The same idea later moved to speedboats and then to motor vehicles, where a rear spoiler is meant to keep a fast car from lifting off the road. Italian, among other languages, later borrowed the English noun for both the aircraft device and the car part.
Sports and politics took another branch. Boxing had used spoiler by the 1930s for a lesser fighter whose tactic is to disrupt an opponent's style. American sports writing had the sense of someone who mars another person's chance at victory by about 1950; politics had it by the late 1950s. A spoiler candidate is not expected to finish first. The damage is the point: enough support siphoned away that the rival who might have won does not.
The plot sense is newer, and reference works do not all date it the same way. Some dictionaries put the movie-and-book sense around 1982. Others place it in the 1970s. Independent historical work, later repeated in newspaper accounts, points to April 1971: Douglas Kenney's National Lampoon piece titled Spoilers, a mock public service that handed readers the endings of thrillers and classics so they would not have to endure suspense. That joke treated spoilers as a product you could collect. A decade later, in 1982, users of Usenet were already putting spoiler alert in front of details from Star Trek II, days after the film opened. The Oxford English Dictionary dates the warning phrase itself to that year. Online etiquette made the formula famous. The noun had already been doing the work in print.
The hide still shows
If one older form holds the later senses together, it is Latin spolium. The hide comes off the animal. The armor comes off the enemy. The lift comes off the wing. The ending comes off the story. Internet fandom did not invent the insult. It only found a new thing worth stripping, and then taught the rest of the language to warn before the stripping began.