Source : Webster's Revised Unabridged Dictionary (1913)

Mostly \Most"ly\, adv.
   For the greatest part; for the most part; chiefly; in the
   main.

Source : WordNet®

mostly
     adv 1: in large part; mainly or chiefly; "These accounts are
            largely inactive" [syn: {largely}, {for the most part}]
     2: usually; as a rule; "by and large it doesn't rain much here"
        [syn: {by and large}, {generally}, {more often than not}]