From BiblePortal Wikipedia

King James Dictionary [1]

Just'Ly, adv. from just. In conformity to law, justice or propriety by right. The offender is justly condemned. The hero is justly rewarded, applauded or honored.

1. According to truth and facts. His character is justly described. 2. Honestly fairly with integrity as, to do justly.  Micah 6 3. Properly accurately exactly.

Their feet assist their hands, and justly beat the ground.

Webster's Dictionary [2]

(a.) In a just manner; in conformity to law, justice, or propriety; by right; honestly; fairly; accurately.