Source : Webster's Revised Unabridged Dictionary (1913)

Casually \Cas"u*al*ly\, adv.
   Without design; accidentally; fortuitously; by chance;
   occasionally.

Source : WordNet®

casually
     adv 1: not methodically or according to plan; "he dealt with his
            course work casually"
     2: in an unconcerned manner; "glanced casually at the
        headlines" [syn: {nonchalantly}]