What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
1A sea serpent or other mythical aquatic creature. Formerly also: a water snake or sea snake.
2Astronomy. With capital initials. The southern constellation Hydra.
Mid 16th century; earliest use found in John Palsgrave (d. 1554), teacher and scholar of languages. From water + serpent.