Latin abbatissa 'abbess'.
While this was more usually found as a title, there are a handful of English occurrences of it used as a given name.
Cite as: J. Uckelman, S.L. Uckelman. "Abbatissa". In S.L. Uckelman, ed. The Dictionary of Medieval Names from European Sources, Edition 2016, no. 4. http://dmnes.org/2016/4/name/Abbatissa.