Source : Webster's Revised Unabridged Dictionary (1913)

Serious \Se"ri*ous\, a. [L. serius: cf. F. s['e]rieux, LL.
   seriosus.]
   1. Grave in manner or disposition; earnest; thoughtful;
      solemn; not light, gay, or volatile.

            He is always serious, yet there is about his manner
            a graceful ease.                      --Macaulay.

   2. Really intending what is said; being in earnest; not
      jesting or deceiving. --Beaconsfield.

   3. Important; weighty; not trifling; grave.

            The holy Scriptures bring to our ears the most
            serious things in the world.          --Young.

   4. Hence, giving rise to apprehension; attended with danger;
      as, a serious injury.

   Syn: Grave; solemn; earnest; sedate; important; weighty. See
        {Grave}. -- {Se"ri*ous*ly}, adv. -- {Se"ri*ous*ness}, n.

Source : WordNet®

seriously
     adv 1: in a serious manner; "talking earnestly with his son"; "she
            started studying snakes in earnest"; "a play dealing
            seriously with the question of divorce" [syn: {earnestly},
             {in earnest}]
     2: to a severe or serious degree; "fingers so badly frozen they
        had to be amputated"; "badly injured"; "a severely
        impaired heart"; "is gravely ill"; "was seriously ill"
        [syn: {badly}, {severely}, {gravely}]