Read the dictionary definition of serious. All definitions for this word.
1. causing fear or anxiety by threatening great harm
1. a dangerous operation
2. a grave situation
3. a grave illness
4. grievous bodily harm
5. a serious wound
6. a serious turn of events
7. a severe case of pneumonia
8. a life-threatening disease
2. requiring effort or concentration; complex and not easy to answer or solve
1. raised serious objections to the proposal
2. the plan has a serious flaw
3. of great consequence
1. marriage is a serious matter
4. appealing to the mind
1. good music
2. a serious book
5. concerned with work or important matters rather than play or trivialities
1. a serious student of history
2. a serious attempt to learn to ski
3. gave me a serious look
4. a serious young man
5. are you serious or joking?
6. Don't be so serious!
6. completely lacking in playfulness