Source : Webster's Revised Unabridged Dictionary (1913)

Chiefly \Chief"ly\, adv.
   1. In the first place; principally; pre["e]minently; above;
      especially.

            Search through this garden; leave unsearched no
            nook; But chiefly where those two fair creatures
            lodge.                                --Milton.

   2. For the most part; mostly.

            Those parts of the kingdom where the . . . estates
            of the dissenters chiefly lay.        --Swift.

Source : WordNet®

chiefly
     adv : for the most part; "he is mainly interested in butterflies"
           [syn: {principally}, {primarily}, {mainly}, {in the
           main}]