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
Kori Rumore, Chicago Tribune, 23 May 2026
Russia is nowhere near a breakthrough in the war — even if Putin continues to pretend otherwise.
—Daniel Depetris, Mercury News, 23 May 2026
Jordan Puente, Los Angeles Times, 18 May 2026
The Knicks look like a team that’s been through multiple playoff battles and knows that now is its time to break through.
—Tony Jones, New York Times, 18 May 2026
See All Example Sentences for breakthrough
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Noun
Chicago’s role in the breakthrough experiment wasn’t revealed publicly until after the first atomic bomb was dropped on Japan — nearly three years later.
—Kori Rumore, Chicago Tribune, 23 May 2026
Russia is nowhere near a breakthrough in the war — even if Putin continues to pretend otherwise.
—Daniel Depetris, Mercury News, 23 May 2026
Verb
South Carolina broke through on an RBI single from left fielder Quincee Lilio to cut UCLA’s lead to 6-1 in the fifth inning after being held to just one hit since the first inning.
—Jordan Puente, Los Angeles Times, 18 May 2026
The Knicks look like a team that’s been through multiple playoff battles and knows that now is its time to break through.
—Tony Jones, New York Times, 18 May 2026
See All Example Sentences for breakthrough
Cite this Entry
“Breakthrough.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/breakthrough. Accessed 24 May. 2026.
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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