The Collaborative International Dictionary of English v.0.48:

Densimeter \Den*sim"e*ter\, n. [L. densus dense + -meter: cf. F.
   densim[`e]tre.]
   An instrument for ascertaining the specific gravity or
   density of a substance.
   [1913 Webster]

WordNet (r) 3.0 (2006):

densimeter
    n 1: a measuring instrument for determining density or specific
         gravity [syn: densimeter, densitometer]