What is the meaning of Sério?

alternative form of seriós

serious; solemn (without humor or expression of happiness)

serious (needing great attention; leaving no room for play)

dangerous

which can’t be joked about; no laughing matter

grave

in a serious manner; in a manner concerning serious matters

in a manner concerning serious matters

A game in which two people stare at each other and the first one to laugh loses.

really? (indicates surprise at, or requesting confirmation of some new information)

Source: wiktionary.org