femina

Femina, feminae, f., first declension. The root is the one behind felix and fecundus and means something like "she who suckles", which is why the word works for the female of any species, animals included, and why it can stand as an adjective: femina equa, a mare.

Against it stands mulier, the social word for a grown woman as opposed to a girl. Classical prose keeps the two apart reasonably well; later Latin does not, and this corpus uses them almost interchangeably. The spelling foemina, everywhere in medieval manuscripts and early printed books, comes from a mistaken link with foetus and is the same word wearing a wrong hat. French femme and Spanish hembra both descend from it.