"something which shocks or excites," especially "a vulgarly exciting tale or description," 1824, agent noun from shock (v.1).
Entries linking to shocker
shock v.1
"to come into violent contact; strike against suddenly and violently," 1560s, literal senses now archaic or obsolete, from shock (n.1). The meaning "offend, displease, strike with indignation, horror, or disgust" is by 1650s. The meaning "to give (something) an electric shock" is from 1746.