For no apparent reason, I was pondering lost temporal words, so I paid a quick visit to ChatGPT and wanted to share the wealth. Perhaps we can bring some of these back from the grave.
Eldernight: Referring to the night before last, this term has long since faded from common usage.
Erewhile: Meaning “a little while ago” or “previously.”
Ereyesterday: Meaning “the day before yesterday” – a direct counterpart to “overmorrow.”
Erstwhile: Similar to “erewhile,” it denotes something that was formerly the case.
Fortnight: Short for “fourteen nights,” this term refers to a two-week period and is still in use in British English.
Nudiustertian: A wonderfully specific Latin-derived term meaning “of or relating to the day before yesterday.”
Overmorrow: This term was used to indicate the day after tomorrow.
Sennight: Derived from “seven nights,” this word was used to mean a week.
Umwhile: Another Scottish term meaning “at times” or “occasionally” in the past.
Whilom: An archaic term meaning “formerly” or “once upon a time.”
Yore: While you touched on similar concepts with “whilom,” this term specifically means “of long ago” or “of time long past.”
Yestereve: This term referred to the evening of the previous day, essentially what we’d call “last night.”
Yestermorrow: An intriguing word that denoted “yesterday morning.”
Yestreen: A Scottish and Northern English word meaning “yesterday evening” or “last night” – similar to “yestereve” but with different regional origins.
These terms, though largely obsolete, offer a glimpse into the linguistic richness of earlier English, providing nuanced ways to express temporal relationships that have since been lost in modern usage.