Easter bonnet
An Easter bonnet is any new or fancy hat worn at Easter, by tradition. It represents the tail-end of a tradition of wearing new clothes at Easter, in harmony with the renewal of the year and the promise of spiritual renewal and redemption.
The "Easter bonnet" was fixed in popular culture by Irving Berlin, whose frame of reference was the Easter parade in New York City, a festive walkabout that made its way down Fifth Avenue from St. Patrick's Cathedral: