Definitions for wagtailˈwægˌteɪl
Random House Webster's College Dictionary
any of various slim, usu. boldly patterned songbirds of the family Motacillidae, mainly of Eurasia and Africa, having a long tail that wags up and down when the bird is still.
any of several similar birds, as the water thrushes of the genus
Origin of wagtail:
Old World bird having a very long tail that jerks up and down as it walks
Any of various small passerine birds of the family Motacillidae, of the Old World, notable for their long tails.
any one of many species of Old World singing birds belonging to Motacilla and several allied genera of the family Motacillidae. They have the habit of constantly jerking their long tails up and down, whence the name