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

Neuromodulation is necessary for keeping the brain’s activity level in a functional range, preventing it from either flatlining or erupting in seizures. —Ingrid Wickelgren, Quanta Magazine, 30 Jan. 2026

Employee engagement has been in decline since 2020 and, over the past two years, has flatlined at 31% of US employees being actively engaged at work. —Barnaby Lashbrooke, Forbes.com, 30 Jan. 2026

From the start of 2013 through the close of 2019, the ratio of debt to GDP basically flatlined at around 75%. —Shawn Tully, Fortune, 21 Jan. 2026

The scoring punch has flatlined. —Kristian Winfield, New York Daily News, 21 Jan. 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
• 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