What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
1North American. Either of two North American herons, the large Ardea herodias (also more fully "great blue heron") and the small Egretta caerulea (also more fully "little blue heron").
2NZ. The darker, slate-grey form of the eastern reef heron, Egretta sacra; = matuku.
Mid 16th century (in an earlier sense). From blue + heron.