How do I expand my new words when I have reached the top 53?

I have leant a long time,but when i reached the top 53,I have not new words.How can I expand wordlist?

I am confused, too. I started to use this app two days ago, and I found there are only 5366 English words and I can't go any further in English vocabulary building with this app.
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But I don't think this is the end for vocabulary building?

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