The Collaborative International Dictionary of English v.0.48:

Integrator \In"te*gra`tor\, n. (Math. & Mech.)
   That which integrates; esp., an instrument by means of which
   the area of a figure can be measured directly, or its moment
   of inertia, or statical moment, etc., be determined.
   [1913 Webster]

WordNet (r) 3.0 (2006):

integrator
    n 1: a measuring instrument for measuring the area of an
         irregular plane figure [syn: integrator, planimeter]