1. (n.) An instrument for determining the specific gravity (relative density) of a substance, and thus the strength of saline solutions\, etc.

2. (n.) An instrument, variously constructed, used for measuring the velocity or discharge of water, as in rivers, from reservoirs, etc., and called by various specific names according to its construction or use, as tachometer, rheometer, hydrometer, pendulum, etc.; a current gauge.