The Oxford Thesaurus An A-Z Dictionary of Synonyms - seriously adv.

1) gravely, badly, severely, critically: Two men were seriously injured in the explosion. 2) really, honestly, Scout's honour, sincerely, truly, candidly, openly, Colloq joking or kidding aside, no joking or kidding or fooling, cross one's heart (and hope to die) : Seriously, kids, I meant what I said about going to bed on time, or no treats tomorrow at the beach. 3 soberly, earnestly, unquestioningly, without a doubt, at face value: What teacher takes seriously that old story about a grandmother's illness as an excuse for absence?