from
The Collaborative International Dictionary of English v.0.48
Fetus \Fe"tus\ (f[=e]"t[u^]s), n.; pl. {Fetuses}
(f[=e]"t[u^]s*[e^]z). [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 a vertebrate animal in the womb, or in
the egg; often restricted to the later stages in the
development of viviparous and oviparous animals. showing the
main recognizable features of the mature animal, {embryo}
being applied to the earlier stages. [Written also
{f[oe]tus}.]
[1913 Webster]