a train of gears or pulleys in which one or more of the axes revolve about a central axis.
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British Dictionary definitions for epicyclic train
a cluster of gears consisting of a central gearwheel with external teeth (the sun), a coaxial gearwheel of greater diameter with internal teeth (the annulus), and one or more planetary gears engaging with both of them to provide a large gear ratio in a compact space
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012