The Collaborative International Dictionary of English v.0.48:

magneto \mag*ne"to\ (m[a^]g*n[=e]"t[-o]), n.
   A small electric generator with an armature rotating in a
   magnetic field, having a secondary winding that generates a
   high voltage, such as one used to generate a voltage
   sufficient to cause a spark to jump between the poles of a
   spark plug in an internal-combustion engine.
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Magneto- \Mag"net*o-\, pref. [See Magnet.]
   A prefix meaning pertaining to, produced by, or in some way
   connected with, magnetism.
   [1913 Webster] Magneto-electric

WordNet (r) 3.0 (2006):

magneto
    n 1: a small dynamo with a secondary winding that produces a
         high voltage enabling a spark to jump between the poles of
         a spark plug in a gasoline engine [syn: magneto,
         magnetoelectric machine]