hilaris

Greek hilaros (ἱλαρός) meant 'cheerful, merry, in good spirits.' It was a moderate word. A hilaros person was pleasant, not hysterical. The word came from the root *sel-, 'to take, to seize' — cheerfulness was something that seized you, a mild possession by good humor. Aristotle used hilaros to describe the temperament of a well-balanced person.

Latin borrowed the word as hilaris and kept the moderate sense. Cicero wrote of hilaris vultus — a cheerful face. The early Christian church named a saint Hilarius of Poitiers (d. 367), and his name was not a joke. It meant 'the cheerful one.' The festival of St. Hilary gives its name to the Hilary Term at Oxford and several English courts.

English borrowed hilarious in the 1820s, and for a century it meant 'cheerful, mirthful' — not very different from the Greek. The intensification happened in the twentieth century. By the 1940s, hilarious had escalated from 'cheerful' to 'extremely funny, causing uncontrollable laughter.' The word was inflated like a currency until its original value was unrecognizable.

Now hilarious is one of the strongest words in English for 'funny.' No one uses it to mean merely cheerful. The word that Aristotle would have applied to a pleasant dinner companion now describes comedy that makes you lose control of your breathing. Two thousand years of semantic inflation turned a smile into a fit.