What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
Tending to be or becoming rigid or stiff; nearly or rather rigid.
Mid 19th century; earliest use found in Proceedings of the American Academy of Arts and Sciences. From classical Latin rigēscent-, rigēscēns, present participle of rigēscere to become stiff or rigid from rigēre to be stiff + -ēscere.