The lexical hypothesis is like having a big, big box of words. It says that the most important or meaningful words in a language will have their very own special word. It's like having a fancy dress for a very important party.
Now, imagine you have a whole bunch of dresses to choose from, but you can only pick the most beautiful, unique or special one. Those dresses are like words, and like dresses, some words are more special than others.
The people who made the lexical hypothesis noticed that there are lots and lots of words in a language, but some words are used more often than others. That means those commonly used words are really important!
So just like you have a special dress for a very important party, the most special, most commonly used words in a language will have their very own word in the dictionary. That is why when we go to our big box of words, we can use the special words to communicate in the best way possible!