The Collaborative International Dictionary of English v.0.48:

capacitor \ca*pac"i*tor\ (k[.a]*p[a^]s"[i^]*t[~e]r), n.
   a device used in electronic circuits to hold electrical
   charge, consisting of two conducting plates separated by a
   nonconducting (dielectric) medium; it is characterized by its
   capacitance.

   Syn: condenser, electrical condenser.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

capacitor
    n 1: an electrical device characterized by its capacity to store
         an electric charge [syn: capacitor, capacitance,
         condenser, electrical condenser]

The Free On-line Dictionary of Computing (30 December 2018):

capacitor

    An electronic device that can store electrical
   charge.  The charge stored Q in Coulombs is related to the
   capacitance C in Farads and the voltage V across the capacitor
   in Volts by Q = CV.

   The basis of a dynamic RAM cell is a capacitor.  They are
   also used for power-supply smoothing (or "decoupling").  This
   is especially important in digital circuits where a digital
   device switching between states causes a sudden demand for
   current.  Without sufficient local power supply decoupling,
   this current "spike" cannot be supplied directly from the
   power supply due to the inductance of the connectors and so
   will cause a sharp drop in the power supply voltage near the
   switching device.  This can cause other devices to malfunction
   resulting in hard to trace glitches.

   (1995-04-12)