samica

1. (in prison) solitary confinement cell; solitary
   Zbog tuče su ga prebacili u samicu. — They moved him to solitary for fighting.
2. (in a dorm, hospital) single room
   U domu sam dobio sobu samicu. — I got a single room in the dorm.
3. dated single woman
   U selu je živela stara samica koju su svi poštovali. — An old single woman whom everyone respected lived in the village.

In the sense "single woman" the word is rare and sounds literary or folksy; people usually say žena koja živi sama or neudata žena.