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

• check out
• conk (out)
• croak [slang]
• decease
• demise
• depart
• die
• drop
• end
• exit
• expire
• fall
• go
• kick in [slang]
• kick off [slang]
• part
• pass (on)
• pass away
• peg out [chiefly British]
• perish
• pop off
• step out
• succumb

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

Nearly 12 years ago, Randy Travis flatlined three times in the midst of a stroke. —Melissa Ruggieri, USA Today, 9 Apr. 2025

Gas demand has flatlined in recent years, but that dynamic is projected to drive it up by another 6 billion cubic feet per day by decade’s end, per S&P Global. —Saul Elbein, The Hill, 24 Mar. 2025

Industrial Production Industrial Production has flatlined over the past couple of years, finally showing some life in January. —Robert Barone, Forbes, 25 Feb. 2025

Productivity has been flatlining to Victorian-era lows, and sickness is the top reason people stay out of the labor force. —Byprarthana Prakash, Fortune Europe, 21 Mar. 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