also: かみつよ
noun
Refers to the distant past, often in historical or literary contexts. The reading じょうせい is standard; かみつよ is archaic.
上世の遺跡から貴重な土器が発掘された。
Valuable pottery was excavated from the ruins of ancient times.
この風習は上世にまで遡ることができる。
This custom can be traced back to antiquity.
Compound of 上 (early, upper) and 世 (age, era). The exact historical derivation is uncertain, but the spelling is conventionally associated with 'ancient times'.