The name Sydney was found in England, and it means wide/broad island. My opinion on the name is I love it and it’s really cute, I remember I used to have someone in my class named Sydney in 2nd grade.
The name Sydney arose independently in England and is derived from the Old English elements sīd (extensive, wide) and ieg (island in a river, riverside meadow).
I've always understood "Sydney" and "Sidney" to be a corruption of the French pronunciation of St Denis, Saint-Denis which is roughly pronounced "Sen-d'nee".
The name of the English place from which the great Australian city took its name probably means south island in one of the Scandinavian languages -so named during the Viking invasions or it could be from the French Saint Denis.