homo

Homo, hominis is third declension masculine, and the genitive is doing real work here because the stem is homin-, not homo-: hominem, homine, homines, hominum, hominibus.

The sense to hold on to is "human being", not "male". Latin has vir for an adult male, and the pair homo and vir is the sharpest distinction in the whole language for an English reader, because English "man" collapses them. A woman is a homo and is not a vir. Grammatically homo takes masculine agreement whoever it refers to, which is a fact about Latin gender rather than about Roman anthropology, though the Romans were not short of the other kind of assumption either.

The plural homines is the ordinary Latin for "people" and is the natural subject of any general statement. Prefix ne- and you get nemo, "nobody", which is also in this two hundred and supplies the missing cases of nullus. The stem gives human, humane, homicide and homage; the Spanish hombre and French homme are its direct descendants.