Areometer

from The Collaborative International Dictionary of English v.0.48

Areometer \A`re*om"e*ter\ (?; 277), n. [Gr. 'araio`s thin, rare
   + -meter: cf. F. ar['e]om[`e]tre.] (Physics)
   An instrument for measuring the specific gravity of fluids; a
   form hydrometer.
   [1913 Webster] Areometric