Rare term for a crater, especially in astronomical or geological contexts. More commonly expressed as クレーター.
See also: クレーター
月の表面には多くの環状山が見られる。
Many craters can be seen on the surface of the moon.
Compound of 環状 (ring-shaped) and 山 (mountain), literally 'ring-shaped mountain'. The exact historical derivation is uncertain; it is a descriptive term for a crater.