Definition of grey wagtail in US English:

grey wagtail

(US gray wagtail)

noun

  • A migratory Eurasian wagtail, Motacilla cinerea, with a grey back and variable amounts of yellow on the underparts, which typically frequents fast-flowing streams and rivers.

Origin

Late 17th century; earliest use found in Francis Willughby (1635–1672), naturalist.