break·through
ˈbrāk-ˌthrü 
plural breakthroughs
1
a
: a sudden advance especially in knowledge or technique
a medical breakthrough
b
: a person's first notable success
—often used before another noun
a breakthrough novel
the actress's breakthrough performance
2
a
: an act or instance of moving through or beyond an obstacle
a breakthrough in the talks between the region's leaders
a breakthrough agreement
b
: an instance of passing through a barrier or protection
The ice under the surface begins to deteriorate, increasing the risk of breakthroughs.—
Vicki Winger
Vicki Winger
specifically, medical
: infection occurring in someone who is fully vaccinated against an infectious agent
A vaccine breakthrough occurs when a person tests positive for COVID-19 two weeks after being fully vaccinated against the disease … —David Rasbach
—often used before another noun David Rasbach Two other CDC studies of breakthrough cases at nursing homes showed the vaccines protected residents, even when the virus spread through the homes. —Maura Dolan
Maura Dolan … the academy recently recommended that children receive two doses of the chicken pox vaccine, rather than just one, because the additional dose bolsters immunity and may help reduce breakthrough infection. —Maria Raven
Maria Raven 3
warfare
: an offensive military assault that penetrates and carries beyond a defensive line
broke through; broken through; breaking through; breaks through
: to make a breakthrough
Examples of breakthrough in a Sentence
Noun
Researchers say they have made a major breakthrough in cancer treatment.
The police have announced a breakthrough in the murder case.
This job could be the breakthrough she's been waiting for.
Recent Examples on the Web
Paul Grein, Billboard, 25 June 2025
There’s no hint yet of a breakthrough on SALT, though Sen. Markwayne Mullin, R-Okla., predicted one will come soon — and that House Republicans will be able to swallow what the Senate comes up with.
—Burgess Everett, semafor.com, 25 June 2025
Zack Cox, Boston Herald, 24 June 2025
Just one, a 50-year-old ship, can break through 20 feet of ice.
—Michael Albertus, Foreign Affairs, 24 June 2025
See All Example Sentences for breakthrough
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Noun
This year marks the 40th anniversary of Houston’s breakthrough.
—Paul Grein, Billboard, 25 June 2025
There’s no hint yet of a breakthrough on SALT, though Sen. Markwayne Mullin, R-Okla., predicted one will come soon — and that House Republicans will be able to swallow what the Senate comes up with.
—Burgess Everett, semafor.com, 25 June 2025
Verb
Those proved to be great value picks (though Zubac didn’t break through until he was traded from the Lakers to the Clippers).
—Zack Cox, Boston Herald, 24 June 2025
Just one, a 50-year-old ship, can break through 20 feet of ice.
—Michael Albertus, Foreign Affairs, 24 June 2025
See All Example Sentences for breakthrough
Cite this Entry
“Breakthrough.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/breakthrough. Accessed 30 Jun. 2025.
Copy CitationKids Definition
breakthrough
noun
break·through
ˈbrāk-ˌthrü
: a sudden advance in knowledge or technique
a breakthrough in medical science
Medical Definition
breakthrough
noun
break·through
ˈbrāk-ˌthrü
: infection occurring in someone who is fully vaccinated against an infectious agent
—often used before another noun
breakthrough infections
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