in earnest

from WordNet (r) 3.0 (2006)

in earnest
    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:
           {seriously}, {earnestly}, {in earnest}]

from The Collaborative International Dictionary of English v.0.48

Earnest \Ear"nest\ ([~e]r"n[e^]st), n. [AS. eornost, eornest;
   akin to OHG. ernust, G. ernst; cf. Icel. orrosta battle,
   perh. akin to Gr. 'orny`nai to excite, L. oriri to rise.]
   Seriousness; reality; fixed determination; eagerness;
   intentness.
   [1913 Webster]

         Take heed that this jest do not one day turn to
         earnest.                                 --Sir P.
                                                  Sidney.
   [1913 Webster]

         And given in earnest what I begged in jest. --Shak.
   [1913 Webster]

   {In earnest}, serious; seriously; not in jest; earnestly.
      [1913 Webster]