pycnometer
A vessel of precisely known volume used by weighing to determine the specific gravity or relative density of a liquid.
As Galileo showed in his tract La Bilancetta, or “The Little Balance,” a scientist of Archimedes’ stature could have achieved a far more precise result using his own law of buoyancy and an accurate scale, something far more common in the ancient world than a very precise pycnometer, which is used to measure displacement.
Where it comes from
From Ancient Greek πυκνός (puknós, “dense”) and μέτρον (métron, “measure”). By surface analysis, pycno- + -meter.
Adapted from the Wiktionary entry pycnometer (CC BY-SA 4.0).