Countdown viewers were left tittering in front of their TVs when a swear word cropped up during the show.
The daytime quiz show's lexicographer Susie Dent suggested the eight-letter word "gobshite" when Rachel Riley put the letters HGTOIBYES on the board during a letters round.
The programme's host Nick Hewer had asked Dictionary Corner guest Adrian Chiles for the best possible word for the round, joking that Chiles looked "excited" about it.
Chiles then handed it over to Dent, who revealed the swear word.
Surprised, Hewer said: "Are you allowed to say that?"
Dent revealed the dictionary definition to be "vulgar slang, a stupid, foolish or incompetent person".
Viewers of the show, which airs at 2.10pm on Channel 4, took to Twitter to air their shock and joy over the word's appearance.
One viewer said it had made their day, and another wrote: "Countdown is GOING OFFFFFF #gobshite."
"As if the word "gobshite" just featured on countdown. What is going on with the world lol," one commented.
Another said: "Are they allowed to say "gobshite" on countdown? - feeling shocked."
One said the word reminded them of sitcom Father Ted, writing: "So glad I am working at home today and this pops up in the background! Where's Father Jack?#gobshite #countdown."
According to one viewer, the appearance of the word was more akin to the programme's spin-off 8 Out Of 10 Cats Does Countdown, which airs in the evening and is hosted by comedian Jimmy Carr.
"When #countdown takes on an episode of 8 Out Of 10 Does Countdown in the afternoon. #gobshite," they wrote.