fetus The term used for the developing individual in the womb, by convention when it ceases to be called an embryo after about the first two months. The adjective ‘fetal’ is however often applied from an earlier stage to the cellular elements of the embryo during and after implantation in the womb, when distinguishing them from the ‘maternal’ tissue. Again by convention, the baby remains a fetus until birth, when it becomes an infant (or, for a month, a neonate). ‘Foetus’ was the traditional British spelling until recent years.

Stuart Judge

fe·tus / ˈfētəs/ • n. (pl. -tus·es) an unborn offspring of a mammal, in particular an unborn human baby more than eight weeks after conception.

fetus (foetus) (fee-tŭs) n. a mammalian embryo during the later stages of development within the uterus; in humans it is an unborn child from its eighth week of development. f. papyraceous a twin fetus that has died in the uterus and become flattened and mummified.
—fetal adj.

fetus (foetus) Stage of embryo development in a mammal after the main adult features are recognizable. In humans, it dates from about eight weeks after conception. The abortion of a fetus continues to be an emotional debate that involves the rights of the fetus and the mother.

fetus (foetus) The embryo of a mammal, especially a human, when development has reached a stage at which the main features of the adult form are recognizable. In humans the embryo from eight weeks to birth is called a fetus.