Anglicized form of Carolus (see Charles), or of its feminine derivative Carola. It has never been common as a boy's name, and has become even less so since its growth in popularity as a girl's name. This seems to be of relatively recent origin (not being found much before the end of the 19th century). It probably originated as a short form of Caroline.
German and Jewish (Ashkenazic): nickname for someone who performed wonders, from German Wunder ‘miracle’, Middle High German wunderære. The Jewish name is mainly of ornamental origin. The German name can also be from a nickname for a curious or inquisitive person, from Middle High German wunder ‘curiosity’, ‘astonishment’.