serious 5 antonyms and opposites of serious. Adj — Not joking or humorous; solemn in manner. Synonyms for serious austere frightful demure grave earnest grievous lack-laughter thoughtful sad sage saturnine sedate solemn solemncholy sober somber sombre staid stern sweer weightsome weighty Antonyms for serious trifling unimportant jesting gaudy witty ← Back to the full definition of serious
