The concept of species is a construct of language.
Members of the same species can procreate fertile offspring. In some edge cases this definition becomes a little fuzzy, but it is clearly more than just a linguistic construct. A mouse and an elephant won't be able to procreate even if the word "species" didn't exist.
It's quite difficult to pin down a precise definition for species. Even genetic definitions don't work so well. Depending on how it is measured chimps hit around 99% genetic similarity with humans. Nature isn't so kind as to provide clean and concrete delineations for us, at least not that we're currently capable of measuring.