Used as a prefix in technical or formal compounds, especially in geology, history, and biology, to indicate an old or ancient period or form.
The old orogenic belt is a mountain range formed in ancient times.
この化石は古期の地層から発見された。
This fossil was discovered in an ancient stratum.
old orogenic belt; Palaeozoic mountain belt
Compound of 古 (old) and 期 (period). The exact historical derivation is uncertain, but it is used as a technical prefix in modern Japanese.