Fetus \Fe"tus\, n.; pl. Fetuses. [L. fetus, foetus, a bringing forth, brood, offspring, young ones, cf. fetus fruitful, fructified, that is or was filled with young; akin to E. fawn a deer, fecundity, felicity, feminine, female, and prob. to do, or according to others, to be.]

The young or embryo of an animal in the womb, or in the egg; often restricted to the later stages in the development of viviparous and oviparous animals, embryo being applied to the earlier stages. [Written also f[oe]tus.]

Source: Webster's Revised Unabridged Dictionary (1913)