Petra itself is quite rare; most of the feminine forms of this name either derive from French Pierre, usually with a diminutive suffix, or from the derivative Petronilla, q.v.
Cite as: J. Uckelman, S.L. Uckelman. "Petra". In S.L. Uckelman, ed. The Dictionary of Medieval Names from European Sources, Edition 2017, no. 1. http://dmnes.org/2017/1/name/Petra.