serious
     adj 1: 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!" [ant: {frivolous}]
     2: of great consequence; "marriage is a serious matter"
     3: 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"; "a
        life-threatening disease" [syn: {dangerous}, {grave}, {grievous},
         {severe}, {life-threatening}]
     4: appealing to the mind; "good music"; "a serious book" [syn:
        {good}]
     5: completely lacking in playfulness [syn: {unplayful}, {sober}]
        [ant: {playful}]
     6: requiring effort or concentration; complex and not easy to
        answer or solve; "raised serious objections to the
        proposal"; "the plan has a serious flaw"
Source: WordNet® 2.0