to wither and fade: to lose freshness and droop, the way a leaf or flower dries up, sinks down, and falls.
At its heart this word describes a living thing losing its freshness and sinking down. A leaf, a flower, or the grass loses its moisture, droops, and drops away. The picture is not only drying out but drooping and falling.
From that plain image the word reaches further. People, and even the whole land, can be said to wither. Enemies lose their nerve and waste away, and in the prophets the earth itself languishes and fades like a dying plant. The same collapse that overtakes a flower overtakes nations and the ground beneath them.
At its widest the word simply means to wear away or give out. A crumbling mountain wears down and falls, and a person worn past their strength droops and gives out. All of these share one motion: something once firm or fresh sinking, fading, and falling.