Seriousmindednesses may seem like a complicated word, but it simply means the ability to think deeply and seriously about things. In contrast, some antonyms for seriousmindednesses could be frivolity, flippancy, or levity. These words indicate a lack of seriousness or a tendency to approach things in a lighthearted manner. Another antonym could be superficiality, which implies a cursory or shallow understanding of a topic. In some cases, a lack of seriousmindednesses may be beneficial, such as in social situations where humor and light conversation are more appropriate. However, in many situations, being seriousminded is crucial for success and should not be downplayed.