The plot device cliffhanger is first found in print in Variety magazine, a US trade weekly magazine focused on entertainment, in 1930. Instead of its current meaning, the term then meant a movie serial, referencing the cliche of a short ending with a character dangling off a cliff awaiting rescue. Cliffhanger gained its current meaning of “suspenseful situation” in 1950, again by association with that cliche.
Cliffhangers as a plot device are of course far older than that word. The iconic 1914 movie serial The Perils of Pauline includes two shorts that end with the heroine literally hanging off a cliff. Fifty years earlier and one medium over, Charles Dickens’s cliffhanger-laden serial fiction defined the style of the genre by 1860. Over a thousand years before that, أَلْفُ لَيْلَةٍ وَلَيْلَةٌ (Alf Laylah wa-Laylah), meaning “One Thousand and One Nights”, used nightly cliffhangers as its central plot device.
Both cliff and hang have been English words since before English existed. They are probably more than 2000 and less than 4000 years old.