1.
long ago, ancient times, the distant past
Refers to a time very far in the past, much more distant than 昔 alone. Used both for actual historical/prehistoric times and colloquially for things that feel like a long time ago.
大昔、ここは海だった。
Long ago, this place was the sea.
そんなのは大昔の話だよ。
That's ancient history.
大昔の人々はどんな生活をしていたのか、想像するだけでワクワクする。
Just imagining what life was like for people in ancient times is exciting.
大昔 is an emphatic form of 昔, intensified by the prefix 大.
TIME SCALE:
- 昔: a long time ago, the past
- 大昔: a very long time ago, ancient times
USAGE:
Often used in storytelling and history contexts. In casual conversation, 大昔の話 ("that's ancient history") dismisses something as no longer relevant.
The classic fairy tale opening 大昔大昔 is the equivalent of "once upon a time, long, long ago."