What is the antonym of ‘Frivolous’?

The antonym of 'Frivolous' is Serious. The word 'frivolous' describes something or someone lacking in seriousness, importance, or purpose; it often implies a lighthearted, trivial, or even silly attitude or behavior. For instance, a frivolous remark might be one made without much thought or concern for its implications, or a frivolous activity could be one pursued purely for amusement without any significant goal. Therefore, its direct opposite would be something that possesses gravity, earnestness, or deep thought. 'Serious' perfectly captures this meaning, referring to something that is important, thoughtful, earnest, or not joking. While 'silly' and 'trivial' are synonyms or closely related in meaning to 'frivolous', and 'light' can sometimes imply a lack of seriousness, 'serious' stands as the most accurate and direct antonym, representing a complete contrast in demeanor, intent, or significance.