“Gobsmacked” means flabbergasted, astounded, speechless, overawed, or stopped dead in your tracks. In other words, your emotion is much stronger than mere surprise.
“Gobsmacked” is a combination of the northern English and Scottish slang term gob, mouth, with the verb smack. An example is: “I was utterly gobsmacked to hear that a 22-year-old woman from America has put her virginity up for sale.”
Gob has been a slang term for the mouth for four hundred years, used, for example, in phrases like “shut your gob!” to tell somebody to be quiet. It may go back to a Scottish Gaelic word meaning a beak or a mouth. “Gab” is another form of the word, which gives us “gift of the gab.” Then there’s “gobstopper,” a round, hard candy which stops one’s gob from other tasks such as talking.
The word first appeared in print in A Woman of Bangkok, by Jack Reynolds, 1959.
It became popular in the 1980s, because it was used in the scripts of British television series, such as Boys from the Blackstuff and Coronation Street. It was then used in newspapers such as The Times, the Independent and the Guardian. William Safire commented in The New York Times in 2004 that the “locution is sweeping the English world.” The Scottish singer Susan Boyle has used it copiously in interviews.
If I ever get smacked in the gob, I hope it’s because of a nice surprise.