uchronia means an idealized or fictional conception of a particular period of time, especially in the past. Lexicurio rates it Sui generis — a strength score of 88 out of 100.
Why “uchronia” is a great word
UCHRONIA — [Noun] An imaginary or fictional conception of a period of time, especially an idealized past or an alternate history diverging from a single changed event. From French uchronie, modeled after utopie ("utopia"), from Ancient Greek οὐ (ou, "not") + χρόνος (khrónos, "time") + -ia. Unlike utopia (a 'no-place') or alternate history (a narrative genre), uchronia is the specific, theoretical 'no-time'—the poignant shimmer of the road not taken. It is the ghostly architecture of a library consumed before it was built, the phantom sound of a treaty never signed, or the clear, quiet air of a world without a certain plague—a nostalgia for a present that haunts our own, born from a single, adjusted moment.
Etymology
Borrowed from French uchronie, formed after utopie (“utopia”), from Ancient Greek οὐ (ou, “not”) + Ancient Greek χρόνος (khrónos, “time”) + -ia.
noun
- An idealized or fictional conception of a particular period of time, especially in the past.“Mercier's resort to uchronia, on the other hand, initiates a new paradigm for utopian literature not only by setting action in a specific future chronologically connected to our past and present but even more crucially by characterizing that future as one belonging to progress and thus linked causally if not immediately to the reader's time.”
- An imaginary setting of a work of fiction derived from assuming that a single particular real-world event had occurred differently than it did, causing history to differ from then on; alternate timeline.“Alternate or alternative histories—uchronias or counterfactuals, to employ yet two other terms—have gone through a boom-and-bust cycle lately, accruing both merits and demerits. […] S.M. Stirling falls into none of these pitfalls. In fact, his new book is simply the best uchronia in years.”