English

Noun

flatline

1. An unchanging state, as indicated in a graph of a variable over time.
   • 1967 June 17, "Business Outlook", Business Week, part 6, page 23:

     Thus, you hear words like "flatline recession," "improvement at a greatly reduced rate," "economic hiccup," "recessionette," "rolling readjustment" and "the economy is double clutching."

2. Asystole; the absence of heart contractions or brain waves.
   1. The disappearance of the rhythmic peaks displayed on a heart monitor.
   2. The disappearance of brain waves on an electroencephalogram.
      • 1972, Louis Lasagna, "Aging and the field of medicine", in Aging and Society: Aging and the professions, edited by Matilda White Riley and ‎Anne Foner, page 68:

        When brain function ceases, the electroencephalogram shows flatline recordings.

Verb

flatline ‎(third-person singular simple present flatlines, present participle flatlining, simple past and past participle flatlined)

1. (intransitive, of the heart) To stop beating.
2. (intransitive, by extension) To die.
3. To stay at the same level, without development; or, to fall.
   • 2012, The Guardian, National Trust attempts to block £100m Giant's Causeway golf course:

     The economy in Northern Ireland is flatlining and jobs are scarce.