impromptu

The Latin phrase in promptu meant at hand, in readiness, in view. Roman writers used it as an adverbial phrase: Livy wrote in promptu esse (to be ready at hand), and the construction appears throughout classical prose. The phrase fused into a single word in French sometime in the 16th century, losing the space between its parts and becoming impromptu, an adverb meaning without preparation. The fusion preserved the Latin form almost exactly.

English borrowed impromptu from French in the 1660s. The diarist Samuel Pepys used it in 1663, writing of a speech made impromptu. The word arrived as an adverb but quickly acquired adjective and noun functions: one could give an impromptu speech or perform an impromptu, the latter a short musical piece. The speed of this grammatical expansion suggests the word filled a gap; English had extemporaneous and offhand, but neither had the compactness of impromptu.

Musicians adopted the noun use with particular enthusiasm. Franz Schubert wrote four pieces called Impromptus in 1827, and Frédéric Chopin added his own set between 1835 and 1842. The musical genre named something specific: a short composition with the feel of spontaneous invention, usually for solo piano. In practice, these were carefully crafted works that impersonated casualness. The name's etymology, in readiness, is quietly ironic: the impromptu is prepared to seem unprepared.

The word has held its spelling and pronunciation with unusual stability for three and a half centuries. Unlike many Latin loans that were anglicized in vowels or endings, impromptu entered English and stayed exactly as it was. The final u is unusual in English orthography, and it still signals the word's French passage. No reformed spelling ever caught on. The Latin phrase, compressed into nine letters, needed no revision.