[adj] causing fear or anxiety by threatening great harm; "a dangerous operation"; "a grave situation"; "a grave illness"; "grievous bodily harm"; "a serious wound"; "a serious turn of events"; "a severe case of pneumonia"
[adj] requiring effort or concentration; complex and not easy to answer or solve; "raised serious objections to the proposal"; "the plan has a serious flaw"
[adj] of great consequence; "marriage is a serious matter"
[adj] appealing to the mind; "good music"; "a serious book"
[adj] 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!"
[adj] completely lacking in playfulness
capital, critical, dangerous, difficult, earnest, good, grave, grievous, hard, important, in earnest(p), intellectual, of import, overserious, real, sedate, sensible, severe, sincere, sober, sobering, solemn, thoughtful, unplayful