If you are going to debate on word usage, please look up the history of the word.
Fetus has been a part of the English lexicon since the 1300s, which is incidentally around the same time when Christianity (which brought Latin with them) reached Britain.
Just as the word "subhuman" was introduced into the English language in 1785. You see, words and symbolism has subjective meaning. Words and Symbolism is a powerful tool to indoctrinate a society as a whole.
On one hand, in terms of religion (and making this short of breaking the forum rule, but instead, making a subjective point) you see words like "cross" and a symbolism forms in your mind of the cross. It bombards not just the mind, but also the conscience.
Then on the other hand, you have words like "evolution" and "atheism" It evokes the mind and conscience into believing something other than a word like "Creation" and "Deity"
Words has a powerful influence to change society, for better or for worse.
The medical community came up with the word "fetus" because at the time, they didn't believe that a unborn child is considered a "baby". Just as you said, around the year 1300. Other medical words soon followed throughout those years and today you have a mass medical vocabulary to describe not only about an unborn child, but they also named every various stages of life.
Words can bring about healing, but it can also bring about destruction.
Take for example of the indoctrination of "abortion" and it's influences, it has taught society that life has no value to some people. Take teenagers and young adults giving birth to babies and dumping them in trash cans. Just look up the news. You can also count the numbers of unborn child killed in the abortion mills, 40 million to be exact. If that's not genocide, then what is it?
Take the words "assisted suicide", people who are terminally ill are indoctrinated that even if while they are in so much pain, the indoctrination instilled into the mind of the patient believes there is no value in continuing life, irregardless of how what one might feel about the patient, whether it be from a family member or a close friend, that it's ok to kill themselves. It won't matter if the family member or friend agrees with it or not.
Words can either teach us to care or become selfish.
Yiz