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”

of great consequence

• “marriage is a serious matter”

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”

appealing to the mind

• “good music”
• “a serious book”

completely lacking in playfulness

requiring effort or concentration; complex and not easy to answer or solve

• “raised serious objections to the proposal”
• “the plan has a serious flaw”