a long time ago; long since
Rare emphatic expression meaning something happened or was the case a very long time ago, often with a nuance of 'already' or 'long since'. Used in colloquial or literary contexts.
It was a dream I had given up on a long time ago.
If it's that story, I've known about it for ages.
Derived from 疾っく (とっく, 'long ago') with the emphatic suffix のとう. The exact origin of のとう is uncertain, but it may be a reduplicative or emphatic extension.