1. (

• 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!" ;

2. (

• serious

) of great consequence; "marriage is a serious matter" ;

3. (

• dangerous ,
• grave ,
• grievous ,
• serious ,
• severe ,
• life-threatening

) 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" ;

4. (

• good ,
• serious

) appealing to the mind; "good music"; "a serious book" ;

5. (

• unplayful ,
• serious ,
• sober ,

) completely lacking in playfulness ;

6. (

• 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" ;