penny dreadful A novel or novelette of mystery, adventure, crime and action.  Without any literary pretensions.  Bound in paper and cheaply printed.  A penny, from the cost; dreadful, presumably, because they were regarded as low, vulgar, sensational etc.  Known among schoolboys as ‘bloods’, and the equivalent of the American dime novel.  G.K. Chesterton wrote a celebrated defence of penny dreadfuls.

[via page 496 of the 1987 edition of Penguin’s A Dictionary of Literary Terms]