cliffhanger, n. — Green’s Dictionary of Slang

cliffhanger n.

[orig. the film description of such silent-era serials as ‘The Perils of Pauline’ (starring Pearl White) in which the heroine, at an episode’s end, was often literally hanging from a cliff]

any suspenseful, threatening situation, although usu. one from which one is eventually delivered.

[1937		‘Variety’ AS XII:4 318/1: Cliff-hangers, type of serial melodrama].
1951		Public Affairs 14-15 lxiii: The affair is becoming like a "cliffhanger" serial.with the denouement tantalisingly postponed from week to week and month to month.
1965		Economist 216:2 807: Callaghan’s Cliffhanger [...] It is a maddening cliffhanger in which the foreign exchange markets and the British authorities are now holding their breath for the next two major instalments.
1968		P. Terson Apprentices (1970) II i: That was a cliffhanger. You came at the right moment.
1977		W. Burrowes Riordans 36: There were several cliffhangers.
1986		F. Taylor Auf Wiedersehen Pet Two 113: That was a blinding game of skittles in the Green Dragon. Right cliff-hanger, that was.
1999		Observer Screen 27 June 3: A huge giant percolator is about to pour boiling hot coffee on them. That was the cliffhanger at the end of the episode.
2000		Guardian Guide 8–14 Jan. 89: Picking up from last season’s will-they-or-won’t-they cliffhanger – it looked like Monica and Chandler were set to tie the knot.