Origin

This character appears to be a compound of two "sun" elements (日) stacked vertically, which most likely symbolizes the passage of time or the turning of days. The doubling emphasizes repetition across time periods, which naturally connected the character to meanings of "formerly" or "once" — referring to something that happened in an earlier cycle of time. Over centuries of use, the visual doubling of the sun became an abstract marker for past experience and temporal distance rather than a literal picture. The sound readings developed separately through Chinese language conventions.