The Collaborative International Dictionary
Magneto-
Magneto- \Mag"net*o-\, pref. [See Magnet.] A prefix meaning pertaining to, produced by, or in some way connected with, magnetism.
Douglas Harper's Etymology Dictionary
magneto-
word-forming element meaning "magnetic, magnetism," from Greek magneto-, combining form of magnes (see magnet).
Wiktionary
magneto-
pre. (alternative form of magnet- English)