The Collaborative International Dictionary of English v.0.48:

Gasometer \Gas*om"e*ter\ (? or ?), n. [Gas + -meter. Cf. F.
   gazom[`e]tre.]
   An apparatus for holding and measuring of gas; in gas works,
   a huge iron cylinder closed at one end and having the other
   end immersed in water, in which it is made to rise or fall,
   according to the volume of gas it contains, or the pressure
   required. Gasometric

WordNet (r) 3.0 (2006):

gasometer
    n 1: a meter for measuring the amount of gas flowing through a
         particular pipe [syn: gas meter, gasometer]
    2: a large gas-tight spherical or cylindrical tank for holding
       gas to be used as fuel [syn: gas holder, gasometer]