The top 1000 most used words in the English language is a much smaller set that you might imagine. But if your goal is to write something that absolutely anyone can get, they’re a good pool to chose from. Here’s my attempt at giving a rough definition of the Trinity used this limited word set:
Trinity – The idea that God is one “being” but three “persons.” The three persons are not “persons” like different human people with totally different minds, wills, and inside thought worlds. Instead, the word “person” here is a picture, an idea that helps you understand the three-in-one. These three persons, the Father, the Son, and the Holy Spirit, are all God. Each of them has been around since before anything (even time!), didn’t come from anything, is just as much God as the others, and does His own kind of thing in the world. That said, they still in some way do everything together. Each one of them is in each other in a way that we can’t really get. They are each and all one and the same God, completely God and the complete God.