serious
adjective
ˈsɪəriəs 
ˈsɪriəs bad
1 bad or dangerousa serious illness/problem/offenceto cause serious injury/damageThey pose a serious threat to security.The consequences could be serious.needing thought
2 needing to be thought about carefully; not only for pleasurea serious articlea serious newspaperIt's time to give serious consideration to this matter.important
3 that must be treated as importantWe need to get down to the serious business of working out costs.The team is a serious contender for the title this year.not silly
4 thinking about things in a careful and sensible way; not sillyBe serious for a moment; this is important.I'm afraid I'm not a very serious person.not joking
5 sincere about something; not joking or meant as a jokeBelieve 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)large amount
6 (informal) used to emphasize that there is a large amount of somethingYou can earn serious money doing that.I'm ready to do some serious eating (= I am very hungry).
Usage note: seriousgrave 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.a(n) serious/grave/earnest/solemn expression/facea serious/solemn mood/atmosphere