adjective

1. of, showing, having, or caused by earnestness or deep thought; earnest, grave, sober, or solemn a serious person
2. 1. meaning what one says or does; not joking or trifling; sincere
   2. meant in earnestness; not said or done in play
3. concerned with grave, important, or complex matters, problems, etc.; weighty a serious novel
4. requiring careful consideration or thought; involving difficulty, effort, or considered action a serious problem
5. giving cause for concern; dangerous a serious wound

Etymology: ME seryows < ML seriosus < L serius, grave, orig., prob. weighty, heavy < ? IE base *swer- > OE swær, heavy, sad, Goth swers, important, orig., heavy