flatline

verb (intr) informal

to die or be so near death that the display of one's vital signs on medical monitoring equipment shows a flat line rather than peaks and troughs
to remain at a continuous low level

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


Word Origin and History for flatline
v.

by 1998, from the flat line on an electrocardiogram or electroencephalogram when the patient is dead. Related: Flatlined; flatlining.

Online Etymology Dictionary, © 2010 Douglas Harper