What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
1with object To subject to melanization; to cause the production or accumulation of melanin in or around (especially as a physiological defence mechanism in insects).
2no object To undergo melanization; to darken as a result of melanin formation.
1960s. From melano- + -ize, after melanized and melanization.