flatline

From flat +‎ line. Refers to a continuous straight line (asystole) on an ECG (EKG) or EEG, indicating death.

• IPA^(key): /ˈflætˌlaɪn/

• Audio (General Australian):

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flatline (plural flatlines)

1. (medicine, cardiology) An 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 Matilda White Riley, Anne Foner, editors, Aging and Society: Aging and the professions, page 68:

        When brain function ceases, the electroencephalogram shows flatline recordings.

2. (also figurative) An unchanging state, as indicated in a graph of a variable over time.
   • 1967 June 17, “Business Outlook”, in 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."

3. (fishing) A line that is run low to the water from the rod tip, generally off a release clip of some type.

• flat line

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

1. (intransitive, medicine, cardiology, of the heart) To stop beating.
2. (intransitive, medicine, cardiology, by extension) To die.
3. (transitive, slang) To kill.
   • 2013, Shobha Nihalani, Nine:

     If looks could kill, Mona's sharp gaze would have flatlined him in one second.

   • 2017, Stephanie Rowe, Not Quite Dead:

     After all she'd been through, she needed sleep and food to heal, not endure a lovemaking session that was so passionate that it had pretty much flatlined him as well.

4. (informal, transitive) To remain 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.

   • 2022 November 16, Mel Holley, “Network News: West Midlands prioritises the return of passsengers”, in RAIL, number 970, page 24:

     But passenger numbers have since recovered to only 85% of pre-March 2020 levels, and growth has flatlined.

5. (of a graph) To experience significantly decreased rates of change compared to previous rates of change.

   Upon upload, the video got 1,000 views/day for the first week, then flatlined and started getting fewer than ten views/day.

6. (fishing, intransitive) To fish using a flatline.

• flatlined (adjectival form)
• flatliner