The Collaborative International Dictionary of English v.0.48:

Cogwheel \Cog"wheel`\, n.
   A wheel with cogs or teeth; a gear wheel. See Illust. of
   Gearing.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cogwheel
    n 1: a toothed wheel that engages another toothed mechanism in
         order to change the speed or direction of transmitted
         motion [syn: gear, gear wheel, geared wheel,
         cogwheel]

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "cogwheel":
   Hydromatic, automatic transmission, differential,
   differential gear, freewheel, gear, gear train, gearbox, gearing,
   gearshift, gearwheel, high, intermediate, low, neutral, overdrive,
   rack, reverse, standard transmission, stick shift, synchromesh,
   transmission