Sinja is a ♀ female name.
Sinja is a Slavic short form of names ending with “-sina/e”, e.g. Theresina and Lusine. But it is as well a variant of the Frisian name Sünje.
Sinja means e.g. “from the island Therassia”, “the huntress”, “summer” (from Theresina) or “moon” (from Lusine). In Frisian it means “little sun”.