What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
A mineral of the triclinic crystal system consisting of a hydrated sulphate of potassium, calcium, and magnesium, K₂Ca₂Mg(SO₄)₄, and usually occurring as pink or red fibrous masses.
Early 19th century; earliest use found in Quarterly Journal Scottish. From German Polyhalit from poly- + ancient Greek ἅλς salt + German -it.