The Collaborative International Dictionary of English v.0.48:

Gravimeter \Gra*vim"e*ter\, n. [L. gravis heavy + -meter: cf. F.
   gravim[`e]tre.] (Physics)
   An instrument for ascertaining the specific gravity of
   bodies.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gravimeter
    n 1: a measuring instrument for determining the specific gravity
         of a liquid or solid [syn: hydrometer, gravimeter]
    2: a measuring instrument for measuring variations in the
       gravitational field of the earth [syn: gravimeter, gravity
       meter]