From The Collaborative International Dictionary of English v.0.48:

electronics \electronics\ n.
   1. the branch of physics that deals with the behavior of
      electrons. Electronics is primarily concerned with
      phenomena other than simple conduction, such as emission
      of electrons, storage of electrical charge, the effects of
      electrical fields on the conduction of electrons through a
      circuit, and amplification and manipulation of electric
      signals such as voltage or current by design of circuits.
      Electronics also encompasses the application of such
      fundamental principles to the construction of devices
      using the manipulation of electrons in their operation,
      known as electronic devices.
      [PJC]

   2. the branch of engineering concerned with design of devices
      using the principles of electronics, for practical
      purposes.
      [PJC]

   3. electronic devices generally, or the electronic circuits
      within an electronic device. The Russian harvesters are
      sturdily constructed, but their electronics are primitive.
      [PJC]

From WordNet (r) 2.0:

electronics
     n : the branch of physics that deals with the emission and
         effects of electrons and with the use of electronic
         devices

From Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "electronics":
   Newtonian physics, acoustics, aerophysics, applied physics,
   astrophysics, basic conductor physics, biophysics,
   chemical physics, cryogenics, crystallography, cytophysics,
   electron physics, electrophysics, geophysics, line radio,
   macrophysics, mathematical physics, mechanics, medicophysics,
   microphysics, natural philosophy, natural science, nuclear physics,
   optics, philosophy, physic, physical chemistry, physical science,
   physicochemistry, physicomathematics, physics, psychophysics,
   radiation physics, radio, radionics, radiophotography,
   radiotelegraphy, radiotelephony, solar physics,
   solid-state physics, statics, stereophysics, television,
   theoretical physics, thermodynamics, wire wave communication,
   wired radio, wired wireless, wireless, wireless telegraphy,
   wireless telephony, zoophysics