to beat or crush to pieces: to pound, hammer, or shatter something with repeated blows.
At its core this is a word for violent, repeated striking that leaves a thing in fragments or in a new shape. It is not a single tap or a passing blow: it is the hammering that grinds an idol to powder, the pounding that smashes a clay pot, the beating that leaves an army broken in the field.
The same action reaches across very different targets. Reformers use it to destroy: Moses pounds the golden calf to dust, Hezekiah smashes the bronze serpent, Josiah beats the idols to powder. Warriors use it to defeat: enemies are beaten down, nations are crushed one against another, and the wicked are broken to pieces between morning and evening. Metalworkers use it to reshape: the raw force of the hammer turns one tool into another.
That last use gives the word its most famous line. In the vision of peace, nations כָּתַת their swords into plowshares, hammering weapons into farm tools. The prophet Joel takes the very same verb and reverses it, ordering the nations to beat their plowshares into swords for war. The word itself carries no verdict of peace or violence: everything depends on what is being beaten into what.
It sits among several Hebrew words for breaking and crushing. It is close to the general verb for shattering, שָׁבַר, and to the verb for pounding something in a mortar, כָּתַשׁ, but its own emphasis falls on beating a thing down until it is in pieces or made over into something else.