Obtund, meaning to dull or blunt sensations or emotions, has a limited number of antonyms to describe its opposite meanings. First, sharpen or intensify could be considered antonyms as they convey the idea of making something more acute or severe. Second, heighten, amplify or magnify could be used as antonyms, where the meaning is to enhance, augment or intensify. Third, inflame or provoke, where the idea is to exaggerate or excite something into being more sensitive. Other words unlikely to be considered antonyms for obtund would be calm, tranquilize or sedate, which have, of course, opposite meanings of what obtund does.