The Collaborative International Dictionary
Pycnometer
Pycnometer \Pyc*nom"e*ter\, n. [Gr. ? dense, compact + -meter.] (Physics) A specific gravity bottle; a standard flask for measuring and comparing the densities of liquids. [Also written pyknometer.]
Wiktionary
pycnometer
n. (context physics English) A (l/en: vessel) used to determine the (l/en: specific gravity) of a (l/en: liquid); a (l/en: specific gravity bottle).