The phrase "doest one in" is an archaic way of saying "do one in" or "do someone in," meaning to harm or kill someone. There are numerous synonyms for this phrase, including "murder," "assassinate," "slay," "eliminate," "terminate," "dispatch," "execute," and "destroy." All of these words suggest a deliberate and often violent act of causing harm or ending a life. While the phrase "doest one in" may sound old-fashioned or outdated, the concepts of violence and harm are still very much present in our society today, and it is important to have language to express them accurately and appropriate in both contemporary and historical contexts.