Source : Webster's Revised Unabridged Dictionary (1913)

Tracheophonae \Tra`che*oph"o*n[ae]\, n. pl. [NL., from trachea +
   Gr. fonei^n to sound.] (Zo["o]l.)
   A group of passerine birds having the syrinx at the lower end
   of the trachea.