What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
1US a person who exchanges a sum of money for the same sum in a different denomination, especially as a profession; (also) any of various machines that perform such an exchange, typically banknotes for coins (now rare).
2A person who works actively to effect positive social change.
Mid 19th century; earliest use found in Knickerbocker.