serious

Synonyms: austere bound bound and determined businesslike cold sober contemplative deadpan deliberate determined downbeat earnest funereal genuine go for broke grave grim honest intent long-faced meditative no-nonsense pensive pokerfaced reflective resolute resolved sedate set severe sincere sober solemn staid steady stern thoughtful unhumorous unsmiling weighty

Antonyms: flippant funny happy light

Synonyms: arduous dangerous deep difficult far-reaching fateful fell formidable grave grievous grim hard heavy important laborious major meaning business meaningful menacing momentous no joke no laughing matter of consequence operose out for blood playing hard ball pressing severe significant smoking sobering strenuous strictly business threatening tough ugly unamusing unhumorous urgent worrying

Antonyms: light minor trivial unimportant unserious