Definitions

1. adjective

Not producing sound; relating to or characterized by a lack of sound, especially in the case of a river or stream that flows underground or through a solid rock.

“The geologist explained that the cave’s underground river was aphonous, meaning it flowed silently without making a sound.”

2. noun

A river or stream that flows underground or through a solid rock.

“The hikers encountered an aphonous river as they descended into the cave, its water flowing silently beneath their feet.”