fetus

American  

[fee-tuhs] / ˈfi təs /

especially British, foetus

noun

Embryology.

plural

fetuses

1. (used chiefly of viviparous mammals) the young of an animal in the womb or egg, especially in the later stages of development when the body structures are in the recognizable form of its kind, in humans after the end of the second month of gestation.

---

fetus British  

/ ˈfiːtəs /

noun

1. the embryo of a mammal in the later stages of development, when it shows all the main recognizable features of the mature animal, esp a human embryo from the end of the second month of pregnancy until birth Compare embryo

---

fetus Scientific  

/ fē′təs /

1. The unborn offspring of a mammal at the later stages of its development, especially a human from eight weeks after fertilization to its birth. In a fetus, all major body organs are present.

---

fetus Cultural  

1. The embryo of an animal that bears its young alive (rather than laying eggs). In humans, the embryo is called a fetus after all major body structures have formed; this stage is reached about sixty days after fertilization.

---

Etymology

Origin of fetus

First recorded in 1350–1400; Middle English, from Latin fētus “bringing forth of young,” hence “that which is born, offspring, young still in the womb,” equivalent to fē- (verb base attested in Latin only in noun derivatives, as fēmina “woman,” fēcundus “fertile,” fīlius “son,” fīlia “daughter,” etc.; compare Greek thēsthai “to suck, milk,” Old High German tāan “to suck,” Old Irish denid “(he) sucks,” Slavic (Polish) doić “to milk” + -tus suffix of verb action; see fecund

Explanation

A fetus is a mammal before it's born. Once upon a time, you started as an embryo, matured into a fetus, and were then thrust into the world as a newborn. Fetus is a Latin word that means "the bearing, bringing forth, or hatching of young." Even though the Latin points to a fetus "hatching," contemporary science only regards viviparous vertebrates as having fetuses. In other words, if an animal has a backbone and was delivered via live birth, it was once a fetus. If a kitten has claws, whiskers, and ears, but is still inside its mother's womb, it's a fetus. In the UK, fetus is spelled foetus.

Example Sentences

Included in the slideshow they posted Thursday is what appears to be a sonogram image of a fetus in a womb, throwing a “rock on” hand signal.

From Los Angeles Times • May 14, 2026

She died with her fetus still in her womb.

From Salon • Apr. 20, 2026

Scientists have shown that this ratio reflects the balance of estrogen and testosterone a fetus is exposed to during the first trimester of pregnancy.

From Science Daily • Feb. 10, 2026

Conversely, maternal cells circulating in the pregnant mother’s bloodstream commonly slip through into the fetus and get incorporated into its body.

From The Wall Street Journal • Nov. 4, 2025

I guess it's not necessarily a bad thing to have a little fetus sibling.

From "Simon vs. the Homo Sapiens Agenda" by Becky Albertalli