serious -
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!"
frivolous not serious in content or attitude or behavior; "a frivolous novel"; "a frivolous remark"; "a frivolous young woman"
sincere,
solemn,
earnest open and genuine; not deceitful; "he was a good man, decent and sincere"; "felt sincere regret that they were leaving"; "sincere friendship"
sobering tending to make sober or more serious; "the news had a sobering effect"
serious -
of great consequence; "marriage is a serious matter"
of import,
important of great significance or value; "important people"; "the important questions of the day"
serious -
requiring effort or concentration; complex and not easy to answer or solve; "raised serious objections to the proposal"; "the plan has a serious flaw"
