Eighty-six is slang meaning “to throw out,” “to get rid of,” or “to refuse service to.” It comes from 1930s soda-counter slang meaning that an item was sold out. There is varying anecdotal evidence about why the term eighty-six was used, but the most common theory is that it is rhyming slang for nix.
Among the most recent senses adopted is a logical extension of the previous ones, with the meaning of “to kill.” We do not enter this sense, due to its relative recency and sparseness of use.
https://www.merriam-webster.com/wordplay/eighty-six-meaning-origin
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