A key is something that gives you access to or helps you to achieve something. Key to happiness is a popular phrase used to refer to something that gives you happiness.
The key to getting good marks is studying. If you form positive study habits you will be successful in every subject.
Chocolate is the key to happiness. I would happily eat it for breakfast, lunch, and dinner every day!
The word key can also be used to refer to a metal object that can be inserted into a lock to open it. Sometimes, in the school setting the word key is used to describe the list of answers to an assignment or test.
Do you have your house key? The front door is locked, and I do not want to have to climb in a window.
The exam was very difficult, and all the students needed the teacher's answer key when correcting their papers.
The word significant means important or having a lot of meaning. It indicates something of consequence. The popular phrase significant other refers to a girlfriend or boyfriend who is important to you.
My significant other lives in another city. We only see each other at weekends after the working week has ended.
In the world of statistics, significant refers to an observation or occurrence that could not have happened by accident.
The test results in Mrs. Smith's class were significant for the number of passing grades. It was clear that the teacher had done a good job presenting the material.
The data taken from the results of our class's chemistry experiment was significant. It indicated that those chemicals were dangerous to humans.