The Collaborative International Dictionary of English v.0.48:

Piezometer \Pi`e*zom"e*ter\, n. [Gr. ? to press + -meter: cf. F.
   pi['e]zom[`e]tre.]
   1. (Physics) An instrument for measuring the compressibility
      of liquids.
      [1913 Webster]

   2. (Physics) A gauge connected with a water main to show the
      pressure at that point.
      [1913 Webster] Piffero

WordNet (r) 3.0 (2006):

piezometer
    n 1: a measuring instrument for measuring high pressures