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
Evan MacDonald, Houston Chronicle, 13 Feb. 2026
If you’re drawn to stories about rediscovery and hidden-in-plain-sight breakthroughs, this one delivers.
—Ryan Brennan, Kansas City Star, 13 Feb. 2026
Dan Santaromita, New York Times, 9 Feb. 2026
The artist broke through to a mainstream American audience via collaborations with artists like Cardi B and Drake.
—Jake Angelo, Fortune, 8 Feb. 2026
See All Example Sentences for breakthrough
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Noun
His work often focuses on patients who rely on the Texas Medical Center, medical breakthroughs and the health care professionals who work in the largest medical center in the world.
—Evan MacDonald, Houston Chronicle, 13 Feb. 2026
If you’re drawn to stories about rediscovery and hidden-in-plain-sight breakthroughs, this one delivers.
—Ryan Brennan, Kansas City Star, 13 Feb. 2026
Verb
Can Justin Herbert finally break through in the postseason?
—Dan Santaromita, New York Times, 9 Feb. 2026
The artist broke through to a mainstream American audience via collaborations with artists like Cardi B and Drake.
—Jake Angelo, Fortune, 8 Feb. 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 14 Feb. 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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