The Collaborative International Dictionary
Night letter
Night letter \Night letter\, Night lettergram \Night lettergram\ See Letter, above.
Wiktionary
night letter
n. an unsigned leaflet distributed clandestinely
WordNet
night letter
n. a cheaper form of telegram sent for delivery the next day
Wikipedia
Night letter
A night letter is an unsigned leaflet distributed clandestinely.
Night Letter (album)
Night Letter is an album by saxophonist Sonny Stitt recorded in 1969 and released on the Prestige label. The album features Stitt using the varitone, an electronic amplification device which altered the saxophone's sound.