A prefix meaning with or together. A slang abbreviation for confidence, as in con man or con game. To con someone is to deceive or take advantage of a person through FRAUD or trickery after winning the person's confidence. Con is also used as a slang abbreviation for convict, as in ex-con to mean someone previously incarcerated. An abbreviation for contra, which means against. To show the pros and cons of a particular issue means to present arguments or evidence on both sides.