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 of flatline

• die
• fall

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

Leaders become the bottleneck, the team defaults to the law of least effort, and performance flatlines. —Expert Panel®, Forbes.com, 28 May 2026

After a busy April that featured multiple severe weather outbreaks across the United States, tornado activity has flatlined this month. —Matthew Cappucci, Washington Post, 26 May 2026

However, in practice, the drama of this World War II spy saga seldom lives up to the filmmaker’s lofty aesthetic goals, resulting in a tale of torture and human fragility that flatlines long before its central martyr. —Siddhant Adlakha, Variety, 17 May 2026

The stock was essentially dead money from May through August 2025, flatlined around $20-$22 while everything else moved. —Josh Brown,sean Russo, CNBC, 27 Apr. 2026

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
• brucine
• byline

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