* Serious: This is the most common translation and it conveys the meaning of being grave, important, or solemn.
* Earnest: This translation emphasizes sincerity and seriousness of purpose.
* Solemn: This implies seriousness and formality.
* Formal: This translation emphasizes the seriousness and lack of informality.
The best translation for "serio" will depend on the specific situation and the nuances of the sentence. For example, "un hombre serio" could be translated as "a serious man" or "a solemn man", while "una situación seria" would be translated as "a serious situation".