blastocyst

noun

blas·​to·​cyst ˈbla-stə-ˌsist How to pronounce blastocyst (audio)
: the modified blastula of a placental mammal having an outer layer composed of the trophoblast

Examples of blastocyst in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
With this defining feature, the zygote becomes a blastocyst, ready to embed itself in the lining of the uterus. — Clare Watson, Quanta Magazine, 27 Feb. 2026 There’s also the waiting period—waiting to see if and how many eggs would fertilize and how many would make it to the blastocyst stage, which happens about five to six days after the sperm fertilizes the egg. — Anna Halkidis, Parents, 9 Dec. 2025 Nine percent of the resulting embryos developed to the blastocyst stage, which is when embryos would be transferred into a woman's womb, the researchers reported. — Rob Stein, NPR, 30 Sep. 2025 When sperms managed to reach the eggs, the ensuing early-stage embryos, called blastocysts, initially appeared stronger than their counterparts conceived in gravity. — Tereza Pultarova, Space.com, 27 Mar. 2026 See All Example Sentences for blastocyst

Word History

Etymology

blasto- + -cyst

First Known Use

1876, in the meaning defined above

Time Traveler
The first known use of blastocyst was in 1876

Rhymes for blastocyst

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Browse Nearby Words

blastocone
blastocyst
Blastocystis
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Cite this Entry

“Blastocyst.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/blastocyst. Accessed 7 Jul. 2026.

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Medical Definition

blastocyst

noun
blas·​to·​cyst ˈblas-tə-ˌsist How to pronounce blastocyst (audio)
: the modified blastula of a placental mammal

More from Merriam-Webster on blastocyst

Britannica.com: Encyclopedia article about blastocyst

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