l. (zool.) one of numerous species of small american singing birds, of the genus vireo, as the solitary, or blue-headed (vireo solitarius); the brotherly-love  (v. philadelphicus); the warbling greenlet (v. gilvus); the yellow-throated greenlet (v. flavifrons) and others. see vireo.-any species of cyclorhis, a genus of tropical american birds allied to the tits.