kaḥad

At its most common, this word is about withholding. Someone knows something (a deed, a fact, an answer, a word from God) and either keeps it back or is pressed not to keep it back. That is why it turns up again and again in demands like "do not hide it from me" and in claims like "I have not concealed your faithfulness." It is less about tucking an object out of sight than about refusing, or being asked not to refuse, to tell what one knows.

It also has a quieter, receiving side: something is hidden or escapes notice. Here the point is usually that nothing escapes God. A person's frame, folly, and sins are all said to be not hidden from him.

The same underlying picture, blotting something out so it is not seen or known, is what connects this hiding sense to the word's other, harsher sense of wiping something out of existence altogether (see the separate meaning below).

The same verb carries a second, much heavier sense: to blot something out of existence. It is used of God or an enemy annihilating a nation, of an angel striking down an army, and of a royal house being cut off from the earth. The action is total; it is not merely damaging or removing something but ending it.

It appears just as often in the receiving direction: a people, a city, or the wicked are cut off, are destroyed, perish. Several of these are pictures of judgment, where those marked for ruin are simply allowed to be blotted out.

This sense and the "hide" sense are almost always kept apart by context and by the shape of the verb, and English translations render them so differently that a reader rarely sees the connection. The dictionaries treat them as one word rather than two look-alikes, joined by the single image of effacing, whether from sight or from existence.