/spɔɪl/
[verb] To damage or ruin something so that it is no longer good or enjoyable; also, to treat someone, especially a child, too kindly by giving them everything they want.
Before it meant ruining birthday surprises, 'spoil' literally meant stripping the skin off a defeated enemy.
The word 'spoil' begins its life in the ancient world with the Latin verb 'spoliare', meaning to strip, plunder, or rob. This verb was connected to the Latin noun 'spolium', which referred to the skin or hide stripped from an animal — and, by grim extension, the armour and weapons stripped from a fallen enemy on the battlefield. The image is visceral and violent: soldiers moving across a battlefield, pulling equipment from the dead. From this concrete, physical act of stripping, the word grew to carry the broader meaning of plundering or despoiling an entire place.
From Latin, the word passed into Old French as 'espoillier', carrying the same essential meaning of plundering and looting. This French form made its way into Middle English during the 13th century, arriving in the language during the period of heavy French influence that followed the Norman Conquest of 1066. In its earliest English uses, 'spoil' was firmly a word of war and robbery — you spoiled a city when you ransacked it, and the 'spoils' of war were the goods and valuables taken from a defeated enemy. This sense of 'spoils' as prizes of victory survives clearly in modern English, most famously in the political saying 'to the victor go the spoils'.
Over time, the meaning of the word began to soften and broaden in interesting ways. By the 16th century, 'spoil' had moved away from active plundering and towards the idea of damage and ruin more generally. If something was spoiled, it had been harmed, wrecked, or made useless — the way food goes bad, or a day is ruined by rain. This shift makes perfect sense: when you plunder and strip something, you inevitably damage and destroy it in the process. The violent root quietly became a general-purpose word for ruin.
The sense of spoiling a child — giving them too much, indulging them until they become demanding and ungrateful — appeared in the late 16th and 17th centuries. This usage draws on the idea that excessive kindness 'damages' a child's character in the same way that neglect damages an object. The English proverb 'spare the rod and spoil the child', which became widely known through this period, used the word in exactly this way. It was a moral warning dressed in the same language as rotting fruit.
One of the most modern uses of the word — to 'spoil' a film, book, or television show by revealing plot details before someone has had the chance to experience them — is surprisingly recent, appearing in its current widespread form only in the late 20th century. Yet it connects back perfectly to the word's oldest meaning: to rob someone of something precious. A spoiler does not steal your belongings; it steals your experience of discovery. The Latin soldiers stripping armour from the dead and the internet user posting the ending of a film are, in the long logic of language, doing exactly the same thing.