What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
1A caterpillar of a geometrid moth (family Geometridae), which resembles a stick or twig and typically holds itself erect and motionless on its prolegs when disturbed.
2†a stick insect (family Phasmida) (obsolete).
Mid 19th century; earliest use found in Gardeners' Chronicle.