Here’s an ambiguous sentence for you: “Because of the agency’s oversight, the corporation’s behavior was sanctioned.” Does that mean, “Because the agency oversaw the company’s behavior, they imposed a penalty for some transgression,” or does it mean, “Because the agency was inattentive, they overlooked the misbehavior and gave it their approval by default”? We’ve stumbled into the looking-glass world of contronyms—words that are their own antonyms.
The contronym (also spelled “contranym”) goes by many names, including auto-antonym, antagonym, enantiodrome, self-antonym, antilogy, and Janus word (from the Roman god of beginnings and endings, often depicted with two faces looking in opposite directions). Here are a few of them.
Sanction—which came to English via French, from Latin sanctio(n-) and sancire, “to ratify,”—can mean “give official permission or approval for (an action)” or conversely, “impose a penalty on.”