Antonyms of adj frivolous

1 sense of frivolous

Sense 1
frivolous (vs. serious) -- (not serious in content or attitude or behavior; "a frivolous novel"; "a frivolous remark"; "a frivolous young woman")

serious (vs. frivolous) -- (concerned with work or important matters rather than play or trivialities; "a serious student of history"; "a serious attempt to learn to ski"; "gave me a serious look"; "a serious young man"; "are you serious or joking?"; "Don't be so serious!")
        => earnest, sincere, solemn -- (characterized by a firm and humorless belief in the validity of your opinions; "both sides were deeply in earnest, even passionate"; "an entirely sincere and cruel tyrant"; "a film with a solemn social message")
        => grave, sedate, sober, solemn -- (dignified and somber in manner or character and committed to keeping promises; "a grave God-fearing man"; "a quiet sedate nature"; "as sober as a judge"; "a solemn promise"; "the judge was solemn as he pronounced sentence")
        => overserious -- (excessively serious)
        => real -- (not to be taken lightly; "statistics demonstrate that poverty and unemployment are very real problems"; "to the man sleeping regularly in doorways homelessness is real")
        => thoughtful, serious-minded -- (acting with or showing thought and good sense; "a sensible young man")
        => sobering -- (tending to make sober or more serious; "the news had a sobering effect")
        => solid -- (of a substantial character and not frivolous or superficial; "work of solid scholarship"; "based on solid facts")

Similarity of adj frivolous

1 sense of frivolous

Sense 1
frivolous (vs. serious) -- (not serious in content or attitude or behavior; "a frivolous novel"; "a frivolous remark"; "a frivolous young woman")
       => airheaded, dizzy, empty-headed, featherbrained, giddy, light-headed, lightheaded, silly -- (lacking seriousness; given to frivolity; "a dizzy blonde"; "light-headed teenagers"; "silly giggles")
       => flighty, flyaway, head-in-the-clouds, scatterbrained -- (guided by whim and fancy; "flighty young girls")
       => flippant, light-minded -- (showing inappropriate levity)
       => idle, light -- (silly or trivial; "idle pleasure"; "light banter"; "light idle chatter")
       => light -- (intended primarily as entertainment; not serious or profound; "light verse"; "a light comedy")
       => trivial -- (concerned with trivialities; "a trivial young woman"; "a trivial mind")
          Also See-> superficial#1