to be gripped by dread: to tremble in terror, to strike terror into others, or to hold in reverent awe
This word names raw, body-shaking dread, a step beyond ordinary fear. The picture underneath it is trembling: the shudder that runs through a person face to face with something overwhelming. One verb runs in three directions at once, and Hebrew lets context decide which is meant: the terror a person feels, the terror a person inflicts, and the awe owed to God.
Most often it is the fear felt. It anchors the steadying refrain spoken to Israel on the edge of battle, "do not be terrified," telling a frightened people not to let dread take hold (Deuteronomy 20:3 is one of several). But the same verb can flip to the fear inflicted: God rising "to terrify the earth" (Isaiah 2:19), or an oppressor who will "strike terror no more" (Psalm 10:18). And it can rise higher still, to reverent dread, standing in awe of the God of Israel (Isaiah 29:23) and the God "greatly to be feared" among the holy ones (Psalm 89:7).
Isaiah 8 turns this whole range into a deliberate point. Isaiah tells the people not to dread what everyone around them dreads, but to make the LORD himself their dread. The one trembling word marks both the panic they must let go of and the awe they must hold onto. It sits close to other Hebrew fear words such as יָרֵא and פָּחַד, and it often stands beside חָתַת, "be shattered with dismay," in the same breath.