(of flightless birds) having a breastbone that lacks a keel for the attachment of flight muscles
2.
of or denoting the flightless birds, formerly classified as a group (the Ratitae), that have a flat breastbone, feathers lacking vanes, and reduced wings
noun
3.
a bird, such as an ostrich, kiwi, or rhea, that belongs to this group; a flightless bird