psith·y·rus \ˈsithərəs\noun Etymology: New Latin, from Greek psithykos whispering, twittering 1.capitalized: a genus of large bees resembling bumblebees but lacking the pollen-collecting apparatus and the worker caste and being parasitic in the nests of bumblebees 2.pluralpsithy·ri\-ˌrī\: any bee of the genus Psithyrus