shuddering horror: the sickened jolt that runs through anyone who looks, and the wrecked people who set it off
This word names a reaction, not a ruin. It comes from a verb meaning "to tremble" (זוּעַ), and what it describes is the physical jolt of horror, the shudder that goes through a person at a sight too awful to take in calmly.
Hebrew then lets that shudder stand in for the thing that causes it. Seven of its eight appearances use one fixed sentence: God gives a people over "to be a horror" to all the kingdoms of the earth. The people are not called ruined or emptied or ugly. They are called the shudder itself, named by the effect they now have on everyone who sees them. English has to unpack that into a phrase like "an object of horror," because English will not let a feeling be a person.
That is why the word almost always turns up inside a list of what onlookers do. It sits beside appalled desolation (שַׁמָּה), hissing, cursing, and mockery, and each item names one more reaction of the watching world. Taken together they make a hard point: part of the disaster is being seen in it.
One verse keeps the horror inside the person who feels it. In Isaiah, working out what God's message actually says will be nothing but terror, and there the shudder belongs to the hearer rather than to a nation on display.