Linguist Arika Okrent and illustrator Sean O’Neill of Mental Floss verbally and visually explain through whiteboard animation, the concept of contronyms, words that are spelled and sound the same, but have completely opposite meanings. Such words include cleave, sanction, clip, dust and trim.
Perhaps the most famous of these words is cleave. It can mean split apart or stick together as in how a baby cleaves to its mother. There were originally two different words in Old English, one meaning to adhere or attach, another meaning to split. Over time they both came to be pronounced as cleave. Clip, which can mean hold things together or cut something off, also came from two different words. One was an Old English word meaning to embrace, kind of like what a paper clip makes 2 pieces of paper do. The other was a later Middle English verb for cut off or sever. The more common reason for a contronym is that the same word just went in two meaning directions. Sanction can be an action of approval or penalty. Behavior is sanctioned by the rules or sanctions are imposed for bad behavior. Sanction originally just meant a law or decree. And those can be used to give permission or punishment.