mishor

At its root this word simply names flat land. It is the ground you get when the hills give out: open, even country you can walk or fight or farm across without climbing. Because it is defined against high ground, it often turns up in a direct contrast with mountains and hills, and armies, farmers, and travelers all reckon with the difference.

More than half its appearances are a place name. "The Mishor" is the broad tableland east of the Jordan, the elevated plateau that once belonged to the Amorite king Sihon and was assigned to the tribes of Reuben and Gad. Its towns (Heshbon, Dibon, Medeba, and others) are listed as "the cities of the plain," and later the same plateau is named again when judgment falls on Moab. In these verses the word is close to a proper noun for one specific region, even though English Bibles usually still translate it as "plain" or "tableland."

A near neighbor is עֲרָבָה, the dry rift-valley steppe; both are flat open country, but that word carries a sense of desert barrenness that this one does not.

The same picture of level ground becomes a way of talking about life and character. A path across the plain is smooth and unobstructed, so to be led "on level ground" is to be kept safe, sure-footed, and clear of traps, which is how the Psalms use it when they ask God for guidance past their enemies.

From there it shifts from the road to the person. To deal "levelly" is to deal fairly: to judge without tilting the scales, to rule justly, to speak honestly. So the word describes a king's just reign, God judging the nations fairly, and a faithful teacher who "walked in peace and uprightness." The single image behind all of this is a surface with no bumps or slopes, whether that is the terrain underfoot or the fairness of a verdict.

Hebrew has close companions here: יֹשֶׁר, plain uprightness of character, and מֵישָׁרִים, which is this same idea of evenness used only in the moral sense and never for a place. The Greek εὐθύτης carries the same "straightness" into the New Testament, where it renders this word in a quotation of Psalm 45.