a large, white, usually silent swan (Cygnus olor) with a black knob at the base of its orange bill: originally of the Old World but now present in NE U.S.
See mute swan in American Heritage Dictionary 4
noun
A white swan (Cygnus olor) native to Europe and Asia and widely introduced elsewhere, having an orange bill with a black knob at the base and being much less vocal than most swans.