greed
A selfish desire to have much more than you need.
Greed is an excessive, selfish desire for more than you need, especially when it comes to money or possessions. A greedy person isn't satisfied with having enough: they always want more, even if getting it means others go without.
Imagine two students selling lemonade at a school fundraiser. One keeps a fair share of the profits and makes sure their partner gets an equal amount. The other secretly pockets most of the money, leaving their partner with almost nothing. That second student is acting out of greed. They already have their share, but they want it all.
Greed differs from simply wanting nice things or working hard to succeed. Wanting to earn money for something you've been saving for isn't greedy. Working to improve your situation isn't greedy. Greed means wanting so much that you're willing to take more than your fair share or harm others to get it.
In stories, greedy characters often learn hard lessons. King Midas wished that everything he touched would turn to gold, but his greed meant he couldn't eat or hug his daughter. Greedy people might end up wealthy but friendless, because others eventually recognize that a greedy person cares more about accumulating things than about treating people fairly.
The adjective form is greedy, and you might hear someone called a greedy-guts as a playful insult when they take too many cookies.