* αντικοινωνικός (antikoinōnikós): This is the most common and direct translation. It literally means "against society" and is generally understood to mean antisocial.
* μη κοινωνικός (mi koinōnikós): This translates to "not social" or "unsocial." It's a less strong term than αντικοινωνικός, and might be better suited if you're describing someone who is shy or withdrawn rather than actively hostile towards society.
* A phrase might be necessary to convey a more specific meaning. For example, if you're talking about antisocial *behavior*, you might use a phrase like αντικοινωνική συμπεριφορά (antikoinōnikí symperifora).
Therefore, αντικοινωνικός (antikoinōnikós) is the closest single-word equivalent, but the best choice depends on the context.