Usually I avoid teaching idioms. For most people learning the basics of a language is difficult enough. Native speakers learn idioms by context and examples in which they are used. Even for native speakers, idioms also need to be avoided in formal situations, such as business letters and legal contracts. They also should be avoided when talking to most second-language learners. However these idioms are a good way to end this set of articles on the word one. These idiomatic expressions use the word one in a very fixed sense.
The use of these phrases can be changed depending on the way they are used. The phrase a one-night stand is about two hundred years old and used to refer to a theatre performance for only one evening. However for the last fifty years the meaning has changed to describe a sexual relationship lasting a single night. A modern person reading an older book might mistake the author's meaning.
Many of these expressions are quite modern and were only created in the last hundred years. Most native speakers do not realise how recent these expressions are and how quickly they might be forgotten.
Mr Example came home late and had to confess to his one and only, that he lost all of their honeymoon funds to a one-armed bandit. He tried to explain that it was just one of those things. That he was just one of the boys. He admitted that when he gambles he has a one-track mind. He only went to the bar to buy one for the road, but then saw that one-armed bandit.
If his loved one wants to keep him, she should control the family's money. A person's one and only means their lover or wife, also referred to as his loved one. To say that something is one of those things refers to something unpredictable happening. A one-armed bandit is a gambling device. The phrase one of the boys means that the person is ordinary, friendly, male and does not have upper-class pretensions. A one-track mind describes a person who only thinks about one topic and ignores everything else. The dangerous expression one for the road is a request for another drink of alcohol before driving home. (If he is responsible the drinker should be walking or riding home!) These expressions will only survive if they are popularly used. I hope that last one is forgotten. The drink driving idiom represents too many innocent deaths.