From BiblePortal Wikipedia

King James Dictionary [1]

Chiefly, adv.

1. Principally eminently in the first place.

It chiefly concerns us to obey the divine precepts.

2. For the most part.

In the parts of the kingdom where the estates of the dissenters chiefly lay.

Webster's Dictionary [2]

(1): (adv.) In the first place; principally; preeminently; above; especially.

(2): (adv.) For the most part; mostly.