statolith

This term is a specialized biological descriptor used primarily in zoology and marine biology. It describes a physical structure that functions as a biological accelerometer, allowing simple organisms to perceive "up" from "down" through the interaction of a heavy mineral mass with sensory hair cells.

Because it refers to a specific anatomical structure, it is used in a technical, scientific register. It is rarely encountered in general conversation and is almost exclusively found in academic papers or textbooks discussing the vestibular systems of invertebrates.