Where does the term one-off come from? Among British foundry workers in the 1950s, the number of units produced from a given mold was designated with the word off. So if twenty widgets came off the line, you’d call that batch a twenty-off. A one-off, in turn, refers to a one-of-a-kind object, such as a prototype model. And although Kingsley Amis once called the term an American abomination, make no mistake: We have the UK to thank for one-off. This is part of a complete episode.