Serious-mindedness is a trait that describes a person who is thoughtful, contemplative, and focused. Antonyms for serious-mindedness include frivolousness, levity, and carelessness. Someone who is frivolous lacks seriousness and tends to engage in frivolous activities without much thought. Levity refers to a lack of seriousness or a lightness of tone, often associated with humor or playfulness. Carelessness describes a lack of thought or concern for consequences, often leading to mistakes or errors. Other antonyms for serious-mindedness include nonchalance, apathy, and indifference, all of which describe a lack of seriousness or concern for important matters.