an involuntary, rapid movement of the eyeball, usually from side to side
Webster’s New World College Dictionary, Fourth Edition, compiled by the
editors of Webster’s New World Dictionaries. Copyright © 2010 by Houghton
Mifflin Harcourt. Published by Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'nystagmus'ModL < Gr nystagmos, drowsiness < nystazein, to be sleepy < IE base *sneud-, to sleep