I have a background in science, so I use commonly understood scientific terms.
You have given one dictionary definition, but there are many others that give different definitions of the word. There are also scientific dictionaries that give a different definition again.
I use the word foetus, (this is the way it is spelt in my country and in the UK), when I want to describe the unborn offspring of a human as well as other animals. This forum is debating abortion in human beings, so I use this term, on this forum, to mean an unborn human offspring.