Understanding the origins of English words often helps us to understand their deeper semantic undertones and their proper usage.
Many English words are derived or directly borrowed from Latin. This is especially true of medical terminology.
fetus: (noun, masculine): birth, offspring, produce, bearing of young, young brood, that which is brought forth
Non-technical Modern English translation, with reference to homo sapiens....baby!
Sources: Cassell's Latin Dictionary (1968), Teach Yourself : Latin Dictionary (1992), Pocket Oxford Latin Dictionary (1995).