Source : Webster's Revised Unabridged Dictionary (1913)

Vireo \Vir"e*o\, n. [L., a species of bird.] (Zo["o]l.)
   Any one of numerous species of American singing birds
   belonging to {Vireo} and allied genera of the family
   {Vireonid[ae]}. In many of the species the back is greenish,
   or olive-colored. Called also {greenlet}.

   Note: In the Eastern United States the most common species
         are the white-eyed vireo ({Vireo Noveboracensis}), the
         redeyed vireo ({V. olivaceus}), the blue-headed, or
         solitary, vireo ({V. solitarius}), the warbling vireo
         ({V. gilvus}), and the yellow-throated vireo ({V.
         flavifrons}). All these are noted for the sweetness of
         their songs.