Definition of the word do in

The term "do in" finds its origins in the underworld slang of the 1930s and 40s. It originally referred to the practice of eliminating or killing someone through underhanded or devious means, typically in criminal or gangster circles. The phrase is believed to have been coined as a play on words of the phrase "do over," which refers to repeating an event that has gone wrong. In this context, "do in" would mean to "do over," or in other words, to carry out a criminal act that would lead to the removal or "undoing" of someone. Over time, the meaning of the phrase has evolved to also include less serious applications in everyday speech, where it simply denotes carrying out a task or activity, particularly one that is unpleasant or unwelcome. However, its origins in criminal slang continue to give it a connotation of underhandedness or deceitfulness.