Definition from Wiktionary, the free dictionary
- (idiomatic, Britain, Ireland) A very long time ago, from the beginning or as far back as one can remember.
- That hat dates from the year dot.
- 1989, Phil South, Rage Hard (in Your Sinclair magazine, June 1989) 
- Disk interfaces have been around since the year dot, as people soon realised that the microdrive was unreliable, unstable and generally rubbish for the storage of anything, useless except as a rather small beermat.
- Year Dot, in LookWAYup Translating Dictionary/Thesaurus.