Definition from Wiktionary, the free dictionary
The phrase may originate from a representation of the zeroth or first year of the Common Era CE, or the point between 1 AD and 1 BC (as there is no year 0).
- (idiomatic, UK, dated) A very long time ago, from the beginning or as far back as one can remember.
- That hat dates from the year dot.
- Year Dot, in LookWAYup Translating Dictionary/Thesaurus.