to perish, to be destroyed, to come to a final end; and, when done to someone else, to destroy them or wipe them out.
At its core this word names the moment a person, a people, a thing, or a hope passes out of existence and does not come back. It can describe what happens to someone (they perish, they are destroyed, they are gone) and, in its stronger forms, what one party does to another (they destroy them, they wipe them out, they make them perish). Hebrew lets the same root carry both the dying and the killing, so the difference between perishing and being destroyed is usually a matter of who is acting on whom, not a different idea.
The word is heavier than simply to die. It points to ruin that is total and often deserved: a nation blotted out, a wicked person whose memory is erased, a plan that collapses past recovery. The prophets and the Psalms use it again and again for the fate God brings on the unrepentant, and Deuteronomy warns Israel that they themselves will perish from the land if they turn away. It is the standard word for the end of the wicked, set against the security of the righteous.
A softer thread runs through the same word: to be lost in the sense of going astray, like a sheep that wanders off or donkeys that cannot be found. Here the thing is not destroyed but missing, out of place, beyond its owner's reach. Israel itself is once called a perishing or wandering Aramean, and God is pictured seeking the straying like a shepherd after a lost animal. The shared thread across all of these is the same: something that was present is now gone.