FLATLINE
Etymology
Noun
flatline (plural flatlines)
An unchanging state, as indicated in a graph of a variable over time.
Asystole; the absence of heart contractions or brain waves.
The disappearance of the rhythmic peaks displayed on a heart monitor.
The disappearance of brain waves on an electroencephalogram.
Verb
flatline (third-person singular simple present flatlines, present participle flatlining, simple past and past participle flatlined)
(intransitive, of the heart) To stop beating.
(intransitive, by extension) To die.
(transitive, slang) To kill.
To stay at the same level, without development; or, to fall.
Source: Wiktionary