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