uchronia

Meanings

1. An idealized or fictional conception of a particular period of time, especially in the past.
2. 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.

Etymology

Borrowed from French uchronie, formed after utopie (“utopia”), from Ancient Greek οὐ (ou, “not”) + Ancient Greek χρόνος (khrónos, “time”) + -ia.