The Collaborative International Dictionary of English v.0.48:

Riant \Ri`ant"\, a. [F. riant, p. pr. of rire to laugh, L.
   ridere.]
   Laughing; laughable; exciting gayety; gay; merry; delightful
   to the view, as a landscape.
   [1913 Webster]

         In such cases the sublimity must be drawn from the
         other sources, with a strict caution, howewer, against
         anything light and riant.                --Burke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

riant
    adj 1: showing or feeling mirth or pleasure or happiness;
           "laughing children" [syn: laughing(a), riant]