verb (intransitive) (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

to die

See flatline
Word Origin

from the flat line displayed on a heart monitor when the heart stopped functioning
Usage Note

slang; also flatline n.

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


Dead: The defendant’s face was flatline


To die: State government is in a coma. We’re going to flat-line at any moment

[1980s+; fr the flat line showing no waves, hence no heartbeat, on a heart-monitoring machine]


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  • Flatling

    [flat-ling] /ˈflæt lɪŋ/ adverb, Also, flatlings, British Dialect. 1. in a position; with the side, as of a sword. 2. flatly or positively. adjective 3. Obsolete. dealt with the side. /ˈflætlɪŋ/ adverb 1. in a flat or prostrate position adjective, adverb 2. with the flat side, as of a sword Also (for adv) flatlings

  • Flatly

    [flat] /flæt/ adjective, flatter, flattest. 1. horizontally level: a flat roof. 2. level, even, or without unevenness of surface, as land or tabletops. 3. having a surface that is without marked projections or depressions: a broad, flat face. 4. lying horizontally and at full length, as a person; prostrate: He was flat on the canvas […]

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