Source : Webster's Revised Unabridged Dictionary (1913)

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}.]