The phrase "do one in" is a colloquial British English term meaning to exhaust someone or to cause them to collapse due to exertion. It is spelled as it sounds, with each word pronounced distinctly. "Do" is pronounced as /duː/ and "one" as /wʌn/, while "in" is pronounced as /ɪn/. The term likely originates from the verb "do" and the phrasal verb "do in," which means to kill or defeat someone. Over time, it has taken on a more benign meaning in everyday speech.
The expression "do one in" is an informal idiom that is commonly used in British English. It is an idiomatic phrase that means to exhaust or tire someone out completely, physically or mentally, often resulting in a state of extreme fatigue or depletion. It is often used to describe a situation where a person becomes extremely worn out or drained due to a strenuous activity, task, or demanding circumstance.
The phrase can also be used figuratively to describe situations that have overwhelming or exhausting effects on individuals. For instance, a long day at work may "do one in" by causing extreme tiredness and weakness. Similarly, a challenging exam or a mentally demanding project can "do one in" by leaving someone mentally exhausted.
The term "do one in" carries a connotation of complete or thorough exhaustion, suggesting that the person is left with little energy or capacity to continue with any activity. It is usually used colloquially and might be employed to convey a sense of humor or empathy when one person recognizes another's fatigue or lack of energy.
Overall, "do one in" is an idiomatic phrase that describes a state of extreme exhaustion, whether physical or mental, when an individual is completely worn out or depleted due to a demanding task, activity, or circumstance.