'even-handedly' is formed from the adjective 'even-handed' plus the adverbial suffix '-ly'. 'Even-handed' originates from the idea of holding the scales of justice evenly in both hands, symbolizing fairness.

The term 'even-handed' appeared in English in the 16th century, and the adverbial form 'even-handedly' developed later to describe actions done in an even-handed manner.

Initially, it referred specifically to literal balance or equality, but over time it evolved to mean fairness and impartiality in judgment or action.