a wild shrub or bush, a low woody plant of the untended countryside
This word names an ordinary piece of scenery: a shrub or bush growing wild, the kind of low woody plant that comes up on its own in open or neglected ground rather than being planted and tended. Genesis 2:5 uses it for exactly that contrast, picturing a world so young that no bush of the field had yet sprung up, because no rain had fallen and no one was there to work the ground. The same plain, physical sense carries through every other appearance: Hagar leaves her dying son under one of these bushes in the wilderness (Genesis 21:15), and Job pictures outcasts so destitute that they forage among such bushes for food and huddle under them for shelter (Job 30:4, 7).
Comparative evidence from related ancient languages, especially Akkadian and Syriac, points to a specific kind of shrub behind the general English word "bush," something like wormwood or a similar hardy desert plant, though the Hebrew text itself never pins down an exact species. What the four passages share is not botany but setting: every one of them is wilderness, wasteland, or a field left uncultivated. The bush marks a place at the edge of, or outside, human care and cultivation.
The word looks and sounds identical to a much more common Hebrew word for pouring out troubled thoughts in speech, the root behind שׂיח "to voice what fills the heart" and its noun שׂיח "complaint, troubled musing." That identical spelling is a coincidence, not a family relationship: nothing in how this plant word is used connects it to speaking, complaining, or meditating, and the two are treated by modern reference works as two unrelated words that happen to be written the same way.