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A sudden reddening of the visual field accompanied by severe headache and caused by engorgement of the blood vessels of the head when a person is subjected to a negative force of gravity, as in stunt flying.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
reddened vision and other symptoms caused by a rush of blood to the head in response to negative gravitational stresses
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
a condition experienced by pilots and astronauts in which rapid deceleration or a negative gravity force drives blood to the head, reddening the field of vision.
[1940–45; on the model of blackout]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.