Etymology

From a Russian pet form Со́ня ‎(Sónja), an informal pet form of Со́фья ‎(Sófʹja) or Софи́я ‎(Sofíja, “Sofia, Sophia”), from the Ancient Greek σοφία ‎(sophía, “wisdom”). It was introduced into English through 19th century Russian literature and taken into general use in early twentieth century.