a burning, possessive intensity of feeling stirred when something one claims as one's own is threatened, rivaled, or surpassed
This is one word with a single hot center, even though English splits it into very different-looking words. At its core it names the fierce reaction that rises in a person, or in God, when a bond, a right, or an honor that truly belongs to them is put at risk or eclipsed by someone else. Whether that reaction looks ugly or noble depends entirely on whether the claim behind it is just.
When the claim is selfish, or merely wishes it had what another has, the feeling curdles into envy or suspicion: a husband's rage over a wife he fears has betrayed him, or the sour resentment that eats at a person watching a neighbor prosper. When the claim is rightful, the same heat becomes zeal: a love so committed to what is its own that it will not stand by while that bond is dishonored. This is why the same word can describe a green-eyed grudge in Proverbs and the LORD's white-hot devotion to his people in the prophets.
The thread that ties every use together is exclusivity. This feeling always assumes a relationship or possession that cannot simply be shared out to a rival. That is the heart of the biblical claim that God is jealous: not petty insecurity, but the refusal of the one who made and rescued his people to share their worship with idols. Reading the word well means asking, each time, whose claim is in view and whether it is right.