The Oker () is a river in Lower Saxony, Germany, that has historically formed an important political boundary. It is a left tributary of the River Aller, in length and runs in a generally northerly direction.
Origin and meaning of the name
The river's name was recorded around 830 as Obacra and, later, as Ovokare und Ovakara. The origin of the name is derived from the roots ov- and -akara meaning “upper” (cf. New High German ober-) and “onward rushing” (rendered in German as “Vorwärtsdrängende”)