The surname Mortimer has a Norman origin, deriving from the village of Mortemer, Seine-Maritime, Normandy.
[1] The 12th century abbey of Mortemer at Lisors near Lyons-la-Forêt is assumed to share the same etymological origin, and was granted to the Cistercian order by Henry II in the 1180s.
According to the toponymists Albert Dauzat and later, François de Beaurepaire, there are two possible explanations for such a place name: First, a small pond must have already existed before the land was given to the monks and have already been called Mortemer like the two other Mortemers, because the word mer "pond" was not used anymore beyond the Xth century.
This word is only attested in North-Western France and of Frankish or Saxon origin mari/meri "mere", "lake"; mort(e) "dead" is also quite common to mean "stagnant" (in Port-Mort "the port with stagnant water", Morteau "dead water", etc.).
Through marriage, the Mortimers came close to the English throne during the reign of Richard II, though their royal claim was ignored after Richard II's deposition by his cousin Henry of Bolingbroke in 1399.