to turn: change the direction one is facing or moving, or send something a roundabout way
At its root this word is about a change of direction. A person stops facing or heading one way and turns to face or head another: Joseph turns away from his brothers to weep, Samuel turns to leave, a dying king turns his face to the wall, a king turns to face the assembly and bless them. The same motion belongs to a journey that does not go straight but bends around an obstacle, a territory, or a people.
The geographic uses are the quiet, technical end of this: a tribal boundary line is described as turning, bending around a hill or a spring as a surveyor would trace it. The image is identical to a person turning, just applied to a line on the land instead of a body. Even a river can turn back, as when the poet pictures the Jordan reversing its course.
What holds these together is the simple act of veering off a straight line. It is the everyday, literal core from which the word's grander senses (circling something, surrounding it) grow.