Definition of serious adjective from the Oxford Advanced Learner's Dictionary

      

    serious

     adjective
    adjective
    BrE BrE//ˈsɪəriəs//
     
    ; NAmE NAmE//ˈsɪriəs//
     
     
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    bad
  1. 1  bad or dangerous a serious illness/problem/offence to cause serious injury/damage They pose a serious threat to security. The consequences could be serious.
  2. needing thought
  3. 2  needing to be thought about carefully; not only for pleasure a serious article a serious newspaper It's time to give serious consideration to this matter.
  4. important
  5. 3  that must be treated as important We need to get down to the serious business of working out costs. The team is a serious contender for the title this year.
  6. not silly
  7. 4  thinking about things in a careful and sensible way; not silly Be serious for a moment; this is important. I'm afraid I'm not a very serious person. Synonymsseriousgrave earnest solemnThese words all describe somebody who thinks and behaves carefully and sensibly, but often without much joy or laughter.serious thinking about things in a careful and sensible way; not laughing about something:He’s not really a very serious person. Be serious for a moment; this is important.grave (rather formal) (of a person) serious in manner, as if something sad, important, or worrying has just happened:He looked very grave as he entered the room.earnest serious and sincere:The earnest young doctor answered all our questions.solemn looking or sounding very serious, without smiling; done or said in a very serious and sincere way:Her expression grew solemn. I made a solemn promise that I would return.Patterns a(n) serious/​grave/​earnest/​solemn expression/​face a serious/​solemn mood/​atmosphere
  8. not joking
  9. 5  sincere about something; not joking or meant as a joke Believe me, I'm deadly (= extremely) serious. Don't laugh, it's a serious suggestion. serious (about doing something) Is she serious about wanting to sell the house? serious (about somebody/something) He's really serious about Penny and wants to get engaged. She doesn’t have a serious boyfriend. (informal) You can't be serious! (= you must be joking) You think I did it? Be serious! (= what you suggest is ridiculous)
  10. large amount
  11. 6(informal) used to emphasize that there is a large amount of something You can earn serious money doing that. I'm ready to do some serious eating (= I am very hungry).
  12. Word Origin late Middle English: from Old French serieux or late Latin seriosus, from Latin serius ‘earnest, serious’.Extra examples Are you serious about resigning? By this time the riots were getting serious. Come on, be serious! He became serious all of a sudden. Joe is deadly serious in his beliefs. Please try to stay serious! The crime is considered serious enough to warrant a jail term. These are terribly serious allegations. This situation could be very serious for her. Be serious for a moment; this is important. He admitted to having made a serious error of judgement. He died after suffering from a serious illness. He used to write somewhat serious articles for the university newspaper. He’s not really a very serious person. It’s time for a serious debate about the issue. Please give this matter some serious thought. She was looking at him with a serious expression on her face. Suddenly the conversation turned serious. The speech was interesting, if a little serious for such a young audience. The storm caused serious damage to farm buildings. This book is the first serious study of the subject. Why do you waste your time reading that? It’s hardly a serious newspaper, is it?
See the Oxford Advanced American Dictionary entry: serious