flatline

verb

flat·​line ˈflat-ˌlīn 

flatlined; flatlining; flatlines

intransitive verb

1

a

: to register on an electronic monitor as having no brain waves or heartbeat

b

: die

2

a

: to be in a state of no progress or advancement

b

: to come to an end

flatliner noun

Synonyms

• die
• fall
• perish

Examples of flatline in a Sentence

the patient was fading fast, and doctors expected him to flatline before the night was over

Recent Examples on the Web

Multiple nations now have annihilation-level nuclear assets, and yet, even as the threat continues escalating, public concern has flatlined. —David Rooney, HollywoodReporter, 2 Sep. 2025

While overall ice levels remain far below historical norms, recent observations show that the pace of loss has nearly flatlined since 2005. —Thomas Westerholm, MSNBC Newsweek, 29 Aug. 2025

The German capital has seen tourism largely flatline in recent years, hotel occupancy rates are far below those in Madrid and Paris, and the sector accounts for a significantly smaller proportion of the city’s economy than, say, Rome. —Semafor Staff, semafor.com, 22 Aug. 2025

Our life expectancy has flatlined. —Angela Haupt, Time, 17 Aug. 2025

Word History

First Known Use

1980, in the meaning defined at sense 1a

Rhymes for flatline

• affine
• airline
• align
• aline
• assign
• baseline
• beamline
• benign
• bloodline
• bovine
• byline
• canine

Medical Definition

flatline

intransitive verb

flat·​line ˈflat-ˌlīn 

flatlined; flatlining

1

: to register on an electronic monitor as having no heartbeat or brain waves : to experience cessation of heart contractions or brain wave activity as indicated by a flat line on a electrocardiogram or electroencephalogram

I flatlined on the operating table, but Dr. Bunsom managed to revive me.

—Alison Wright, Yoga Journal

He used to be ill quite a bit as a younger child, and his heart flatlined four times before he was 6.

—Ginnie Graham, Tulsa World

2

: die entry 1

But just because death is expected doesn't mean it's any less depressing when the patient finally flatlines.

—Phil Taylor, Sports Illustrated