"It" /ɪt/ is a third-person, singular neuter pronoun (nominative (subjective) case and oblique (objective) case) in Modern English. --Wikipedia, "It (pronoun)"
"neuter pronoun" links to "Gender-neutral pronoun".
So, we have the word. We just refuse to use it.
I guess I should have specified an anthromorphic, gender-neutral pronoun. It has a long history of referring to non-human things, and when you do use it to refer to humans, it is almost always highly derogatory because the implication is the object of the it isn't human.