Meaning of “seriously” - Learner’s Dictionary

seriously

adverb uk us /ˈsɪəriəsli/
SERIOUS WAY

B1 in a serious way:

seriously injured
Smoking can seriously damage your health.
NOT A JOKE

B2 used to show that what you are going to say is not a joke:

Seriously though, you mustn't say that.
take sb/sth seriously

B2 to believe that someone or something is important and that you should pay attention to them:

The police have to take any terrorist threat seriously.

(Definition of “seriously” from the Cambridge Learner’s Dictionary © Cambridge University Press)