flatbill, any of six species of Central and South American birds belonging to the tyrant flycatcher family Tyrannidae (order Passeriformes). Flatbills, which constitute the genera Rhynchocyclus and Ramphotrigon, are distinguished by their exceptionally broad and flat bill. All are olive, marked with gray, brown, or black above and yellow or brownish below. In length they are 15–17 centimetres (6–7 inches).