Word.ws English Dictionary

flatline

/ˈflætˌlaɪn/

flatline noun: the disappearance of the rhythmic peaks displayed on a heart monitor.

Noun

flatline (plural flatlines)

  1. The disappearance of the rhythmic peaks displayed on a heart monitor.
  2. The disappearance of brain waves on an electroencephalogram.
    • When brain function ceases, the electroencephalogram shows flatline recordings.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
  3. (also, figuratively) An unchanging state, as indicated in a graph of a variable over time.
    • Thus, you hear words like "flatline recession," "improvement at a greatly reduced rate," "economic hiccup," "recessionette," "rolling readjustment" and "the economy is double clutching."1967 June 17, “Business Outlook”, in Business Week, part 6, page 23
  4. A line that is run low to the water from the rod tip, generally off a release clip of some type.

Verb

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

  1. (intransitive) To stop beating.
  2. (broadly, intransitive) To die.
  3. (slang, transitive) To kill.
    • If looks could kill, Mona's sharp gaze would have flatlined him in one second.2013, Shobha Nihalani, Nine
    • 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.2017, Stephanie Rowe, Not Quite Dead
  4. (informal, intransitive) To remain at the same level, without development; or, to fall.
    • The economy in Northern Ireland is flatlining and jobs are scarce.2012, The Guardian, National Trust attempts to block £100m Giant's Causeway golf course
    • But passenger numbers have since recovered to only 85% of pre-March 2020 levels, and growth has flatlined.2022 November 16, Mel Holley, “Network News: West Midlands prioritises the return of passsengers”, in RAIL, number 970, page 24
  5. 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. (intransitive) To fish using a flatline.

Forms of flatline

Noun
pluralflatlines
alternative formflat line
Verb
third-person singular presentflatlines
present participleflatlining
past participleflatlined
pastflatlined

Origin of flatline

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

Words formed from flatline

Questions about flatline

What does flatline mean?
Flatline means the disappearance of the rhythmic peaks displayed on a heart monitor.
What part of speech is flatline?
Flatline can be a noun or a verb.
How do you pronounce flatline?
Flatline is pronounced /ˈflætˌlaɪn/.
What is the plural of flatline?
The plural of flatline is flatlines.

Words near flatline in the dictionary

  1. flatleaf
  2. flatless
  3. flatlet
  4. flatlets
  5. Flatley
  6. flatline
  7. flatlined
  8. flatliner
  9. flatliners
  10. flatlines
  11. flatling

Source and license

Adapted from Wiktionary: flatline (page history and authors). Text available under the Creative Commons Attribution-ShareAlike 4.0 license. Word.ws reformatted the entry and added links. Wiktionary data of 2026-09-02.

Last updated:

Pronunciation audio from Wikimedia Commons, each file under its own free license: En-au-flatline.ogg.

Cite this entry: “flatline.” Word.ws, https://word.ws/flatline. Based on Wiktionary, CC BY-SA 4.0.